Shadowrunner Bob has Strength 4 and is holding an Ares Crusader II in his right hand, so his recoil compensation is 4.
His recoil compensation is 5
(1 free point that everyone get, 2 points from strength / 3 round up and 2 from the in build gas-vent 2)
It's Bob's initiative phase. He has another Ares Crusader II in his holster. He already shot 3-round bursts twice in his previous 2 IPs, so his actual recoil is 6 - 4 =2.
This depend on how progressive recoil actually work (there are some arguments that the rule is ambiguous or even wrong) and if the 3-round burst is a Semi-Automatic Burst complex action or a Burst Fire simple action.
But for sake of argument let us assume that you need to spend a full complex action not shooting anything at all.
6 bullets fired. 5 points of recoil compensation. he had -1 dice on his last attack.
A) If Bob just shoot this one bullet, he will suffer from -3 recoil modifier.
(if he was previously shooting burst fire he first need to spend a simple action to switch from burst fire mode to semi-automatic mode. or as a free action if his weapon have wireless on. If he previously was shooting semi-automatic burst then he doesn't need to switch fire mode)
one more bullet would add up to a total of 7 bullets. 5 points of recoil compensation. -2 dice due to recoil on his semi-automatic simple action.
B) If before shooting, Bob uses a simple action to draw another Ares, but shoot just with one of the Ares, he will suffer from a -1 recoil modifier. RAW, the second readied Ares helps calculating his recoil compensation even if not uses, so the character RC jumps to 6.
We are back at 6 bullets fired?
If you draw a second ares but continue to shoot one bullet with your first ares then you will have 7 bullets and 5 points of recoil compensation. -2 dice due to recoil.
If you draw a second ares and take one shot with the new ares then you will not suffer any additional recoil since the new weapon have enough compensation for two bullets before you start accumulating progressive recoil. recoil, however, is not per weapon - it is per person. so in this case you would still suffer recoil from your first weapon and take -1 dice due to recoil (6 bullets fired compensated by 5 recoil before you pulled your secondary weapon) and you would also take -2 dice from the ranged modifier Attacker using off-hand weapon unless you have the Ambidextrous positive quality.
I know what you are fishing at. But using the recoil compensation from both weapons only apply when you start the fight with both weapons and fire from both weapons. you can't use the recoil compensation of a left hand weapon when you only fire from your right hand...
If you read a bit higher up on the same page it say
"...If you are firing two guns at the same time, shots from the one affect the other, so bullets from each gun add to your total recoil value." and after that they start to talk about recoil penalty and recoil compensation.
If you don't fire your off-hand weapon then you don't get progressive recoil for it and you don't get to take advantage of the recoil compensation.
The example they used is based that you start with 2 drawn and ready firearms and that you even fire both simulations.
Even if you can make it RAW it is 100% not RAI and someone should hit you with the rulebook twice for thinking it out loud

C) Some GM may say that they would house-rule that a weapon RC is used only when the weapon is used. So, lets assume that Bob decides do shoot with both weapons. Even so, recoil modifier: -2.
We are back at 6 bullets I take it?
One bullet from each weapon. That mean you have 7 bullets fired from the first weapon with 5 points of recoil compensation which land you on -2. The 1st bullet from your secondary weapon (or the 9th bullet total) will not cause any extra recoil since that weapon have two points of unused recoil compensation. You still take -2 dice from the ranged modifier Attacker using off-hand weapon unless you have the Ambidextrous positive quality. Since you are not allowed to attack the same target twice (jury is still out on that one i think) you have to split your two attacks at two different targets. -2 for recoil. -2 for off-hand without Ambidextrous. So -4 dice, then split remaining dice pool in half. Resolve as normal.