In theory, the only real barrier that I know of is time. Granted, I'm not certain how much is involved on the back end, so... This is just my own lacking knowledge.
For one, someone needs to type up a set of corrections. Not only pointing them out, but also typing up the correction itself. To give an example, I tend to be a tad faux-dyslexic with my page references when I write. The correct format should be p.XX,
Book Name. I sometimes flip that around. When we were proofing the semi-final version of the FAQ above, we were catching a bunch of those. So when we were fixing those, my proofing notes read like this:
Page 2, Column 1, Third Paragraph, Second Sentence:
"If the players use Marshmallows, drop a Thor Shot on their heads (
War!, p. 272)"
Change To:
"If the players use Marshmallows, drop a Thor Shot on their heads (p. 272,
War!)"
We do this, so that when it gets to the next step, Layout, our Layout guy can find and correct these quickly and easily. Ideally these would be caught in proofing and fixed in the text before it hit layout originally, but... Proofing and editing is often like distilling out impurities. You don't catch everything the first time through, and you have to run it through several times. And sometimes after things go through proofing, you end up making some changes (rewriting portions, moving things around, etc). Which means those portions slip through the earlier proofing process. It's annoying when this happens, but... It happens.
So then the Layout guy has to go through and make all those tweaks. Usually this isn't a problem, but sometimes the changes are semi-significant, involving several lines of text, which can end up shifting multiple pages around. So this can be quite time intensive as well.
And, well, at the end of the day, we're a small operation of very underpaid employees, most of us with day jobs (Or in my case, VERY underpaid and looking desperately for a day job

. Matt Heerdt, who does the layout on Missions, has a regular job plus handles layout for, AFAIK, almost everything CGL does. Between all the Missions stuff I keep dropping on him (one Missions per month so far, plus things like redesigning the cover, tweaking the interiors to prep for Missions going Color, and being a real champ and completely rebuilding and tweaking the Missions Debreifing Logs, the Calender, and the Karma Transfer Log. All stuff he's done this last week for me). Plus he also handles the SR eBooks, the SR core books, and I think all the Battletech stuff (And judging by all the tweets that show up on Facebook, I think BT has been releasing about 14 PDFs a week).
So finding the time to go back and fix things is a giant pain in the arse. Esepcially since no matter how much we get done, there's more piled up in front of us. (Again, using Missions since that's my area, I just finished writing a Mission (SRM 04-00), I'm writing a second one (SRM 04-01), I have 3 final drafts that are being proofed (CMP 2011-01, -02, and -04), one Mission I'm waiting for a the final draft to come in so I can get it proofed (CMP 2011-03), and waiting on a couple more first drafts (SRM 04-02, SRM 04-03, and PM-01). And I'm moving across the state tomorrow and may not have internet access for a couple weeks, so I'm trying to get as much wrapped up as I can tonight so that I can send 4 of those off to layout, send one off to proofing, and send the first drafts back with dev notes, rewrites, and tweaks.
Plus I'm trying to start organizing the conventions since I'm helping with that this year.
And... At some point... I have to go back to some stuff that's technically "done" but not released publicly yet (SMH 2011, and the 8 2010 CMPs) and get them cleaned up so we can figure out how to release those.
And this has been the same sort of schedule I've been under since March when I took over Missions. And I don't expect it to slow down. Ever. Oi vey!
I'm not making excuses. I've been trying to work very hard to catch these errors. I have 3 dedicated proofers, plus the Missions team in general. I post Missions up for comments from the group first, so they can catch any major errors. This is after I've gone back and forth a couple of times on it with the author, reading it over, tweaking it, and making sure things conforms to the rules and is balanced and playable. Then it gets run through one of the proofing staff, and ideally one of the others to double check things (At this stage, it's grammar, punctuation, style, and the little things, as well as one more eye on the text to catch errors).
Then it hits layout, then me and Jason go over it one last time, doing Layout correction notes like I posted above. Then Matt tweaks it, THEN it's released.
And then we find a couple last minute errors, inevitably, and the question becomes "Are these minor enough to ignore, or do we need to fix it". If it's a minor typo or two, it's not worth fixing (I'd love to, but again,time and effort and manpower). If it's major, then IMO yes and I try to get it fixed.
Again, this is just on MY end for Missions. But, as I said above, a lot of the same people are involved with all the SR stuff, so everyone's looking at how we do things to refine them.
Keep posting Errata stuff you guys find in the Errata board. If you can, keep the style I mentioned above in mine when listing errors, to make them quick and easy to catch and fix. I'd love to see corrected PDFs posted myself, and I'd love to see an Errata document posted for people who bought the physical copies of the book. I can't say that this will happen, just that, hey, I'd love to see it, and I can at least pester the right people to see if we can figure out a way to make it happen.
(And hey, if anyone is interested in helping out with this on a purely voluntary basis, let me know.

Bull