[Odsh]

I'm pretty sure in previous editions Dermal Plating and Dermal Deposits didn't stack.

The wording for SR6 is a bit ambiguous though:

Dermal plating cannot be combined with other augmentations to the skin that provide a Defense Rating bonus, including orthoskin.

The ambiguity stems from the term "augmentation" which is never clearly defined.
To me, an "augmentation" in Shadowrun has always designated an implant. An "augmented" metahuman is one that went under the knife to replace and improve parts of his body.
But an "augmentation to the skin" might have a slightly different meaning in this context.

In short: Dermal Deposits is a quality, not a cyberware or bioware implant. Does it count as an "augmentation to the skin"?

Apart from trying to guess RAI, what is your personal experience on this matter? Would you say that allowing them to stack unbalances the game?

[Xenon]

Does it count as an "augmentation to the skin"?

Both the dermal plating cyberare and the dermal deposits quality that trolls come with make the subjects skin stronger.

what is your personal experience on this matter?

In previous edition it was even explicitly stated that orthoskin would replace dermal deposits (and that cybereyes replace natural low light qualities etc).

[Stainless Steel Devil Rat]

My take:

Augmentations are cyberware, bioware, drugs, sustained spells, and adept powers.  The general rule of thumb: if it counts against the augmented bonus limit, it's an augmentation. Of course, that rule of thumb begins to get VERY complicated when it comes to skills, at least in 6e.  But, attribute-wise, at least there it's still fairly cut and dried   Either way, dermal deposits is (imo) not an augmentation, for whatever that matters.

Also:
Xenon is absolutely correct in that 6e cut so many corners in slimming down, sometimes you just have to look at 5e to figure out what they mean in certain contexts. But, on the other hand, sometimes an omission is deliberate.  It can be challenging to tell when an omission is an oversight or a deliberate change.  Dermal plating and orthoskin no longer saying they are incompatible with Dermal deposits could seriously be either.

My opinion:
Just let them stack.  Dermal deposits is giving you all of +1DR higher than you would normally get on top of your augmentation, that's not breaking game balance.  The other benefit to Dermal Deposits, turning unarmed damage from S to P, is likely already made moot elsewhere by some other augmentation anyway if you're building a combat type.  While it makes a degree of sense to say you have to lose the natural body part (like, as Xenon points out, if you have the Low Light quality you should lose it when you get cybereyes) it doesn't seem like it's worth the bother to say you lose Dermal Deposits if you implant Plating or Orthoskin.  Of course, there's nothing wrong with saying you DO... I mean, if you get 2 cyberarms, 2 cyberlegs, cybertorso, and a cyberskull, what's left to still have Dermal Deposits?  The concept of losing the quality due to an augmentation replacing them IS sound... as I said it just doesn't seem there's (much) of a game balance point in saying so in this case.  YMMV.

[Xenon]

Dermal plating and orthoskin no longer saying they are incompatible with Dermal deposits could seriously be either.

Well... to be fair, the description of dermal plating cybernetics and orthoskin bioware didn't explicitly mention that they were incompatible with dermal deposits in previous edition either. It was more of a general statement that was made earlier, that when installing some cyberware and bioware it may remove a particular racial bonus.

SR5 p. 94 Cyberware and Bioware
Note that if a character takes cyberware or bioware, it may remove a particular racial bonus. For example, if a player who has an elf character buys cybereyes, their natural low-light vision is removed and replaced with the cybereyes and whatever attributes it possesses. If the player still wants low-light vision, she’ll have to select the low-light modification for the cybereyes. Similarly, orthoskin replaces the natural dermal deposits of a troll so he would no longer receive the +1 dermal armor from his natural skin hardness.

Cybereyes replace your natural eyes. If you have qualities such as low light vision then it will be replaced when your cybereyes are installed (which mean you need to install a low light cybereye modifications if you still want to keep it)

Orthoskin replace your natural skin. If you have qualities such as dermal deposits then it will be replaced when your orthoskin is installed (which mean I don't think it is right that you would get to double dip bonus defense rating).

Edit: This is at least my answer if OP is looking for an 'official' answer to a rules question.

Having said that, I also fully agree with your opinion SSDR.

[Odsh]

Thanks for your responses.

6e cut so many corners in slimming down, sometimes you just have to look at 5e to figure out what they mean in certain contexts. But, on the other hand, sometimes an omission is deliberate.  It can be challenging to tell when an omission is an oversight or a deliberate change.

My thoughts exactly.

Cybereyes removing low light vision seems obvious.

But one could imagine that in SR6 the intent was that Dermal Deposits keep forming on top of the Orthoskin, or that Dermal Plating is just an additional layer on top of the Dermal Deposits...

Since it's not really game breaking, I think I'll let them combine themselves, if only to avoid trolls losing that innate ability.

[Sphinx]

Orthoskin (SR6 p.292) weaves a network of energy-diffusing biofibers underneath the skin. Dermal plating (p.286) bonds plastic/ceramic-fiber plates onto the skin. Neither actually replaces the skin. The two augmentations are explicitly incompatible with each other, but neither says anything about the dermal deposits quality (p.71). Given the limited utility of Defense Rating in SR6, I'd let them stack.

The original description of orthoskin (SR1 Shadowtech p.17) was the most detailed:
"Orthoskin weaves an energy-diffusing material under the skin that gives the recipient the equivalent of personal armor. The transformation of skin into orthoskin is an extensive process. The individual's skin is peeled back section by section, and the body's dermal layer is fortified by grafts of sythagen (a strengthened and reinforced collagen-protein derivative), flextin (a synthetic and more resilient form of the elastin protein), and flakes of modified and laced cartilage. Much more durable and resistant to damage and environmental extremes, orthoskin gives a character extra levels of both impact and ballistic armor, which are cumulative with externally worn armor. Once transplanted, orthoskin grows like normal skin and is virtually indistinguishable from unaugmented skin; the underlying subdermis is altered at the same time to enable it to sustain the new dermal architecture. An additional bonus from orthoskin is that any damage to the body heals with little or no scarring. A disadvantage is that characters with orthoskin lose some degree of sensitivity of touch because of the increased density of the dermis."

[Xenon]

The individual's skin is peeled back section by section

orthoskin replaces the natural dermal deposits of a troll so he would no longer receive the +1 dermal armor from his natural skin hardness.

Orthoskin weaves a network of energy-diffusing biofibers underneath the skin"

If you peel back the natural dermal deposits section by section to weave a network of energy-diffusion biofibers I don't see why you would still also gain a defense rating from your, now non-existent, dermal deposits (especially since it seem to be clear that your biofibers are also incompatible to binding plastic/ceramic-fiber plates on top of them).

Given the limited utility of Defense Rating in SR6, I'd let them stack.

This is a valid argument. I guess.
But with that reasoning you could also argue that orthoskin and dermal plating should be compatible? ;-)