I think the Ross-Tech guidelines for V94 coding are missing a few things. The coding on my car was originally 16140. If I add up all the possible options listed by Ross-Tech, they don't add up to 16140. At most, I end up with 15215. This is the list provided by Ross-Tech:

+00001 - Rear Lid Opening via Rear Lid Lock
+00002 - Anti-Theft Confirmation via Blink
+00004 - Selective Locking
+00008 - Anti-Theft-System
+00032 - Locking via Speed
+00064 - Comfort Closing via Remote Control
+00256 - Rear Lid Logic
+00512 - Remote Control "Close" Confirmation (1x Blink)
+02048 - Door/Window Logic (USA)
+04096 - Remote Control "Open" Confirmation (2x Blink)
+08192 - Remote Control

Near as I can figure, there's definitely something missing at +01024, and possibly also at +00128. The +01024 thing is something that was enabled on my car by default, but I haven't noticed anything missing since I disabled it, so I really have no clue what it could be. As for +00128, if that does anything at all, it's also a complete mystery.

Anyone know what those things could be?

P.S. My car used to beep when I locked the doors, but hasn't done so in months. I assume the alarm module's battery is dead. It's possible that that's what +01024 is, which would explain why I don't notice any difference now.

 

so... no-one knows? It's a complete mystery?

 

In the absence of any useful information, I just spent a bunch of time trying things randomly and looking for differences. The differences can be so minor as to be nearly invisible, but with a bit of luck, I was able to solve at least some of the mystery.

As I mentioned in my OP, my car was originally coded with 16140. This turns out to be the following options:

+08192 - Remote Control
+04096 - Remote Control "Open" Confirmation (2x Blink)
+02048 - Door/Window Logic (USA)
+01024 - (unknown)
+00512 - Remote Control "Close" Confirmation (1x Blink)
+00256 - Rear Lid Logic
+00008 - Anti-Theft-System
+00004 - Selective Locking

I should point out that on my car, Remote Control "Close" Confirmation does not appear to work at all. No lights blink and no horn sounds when I lock the car using the remote. So it's hard to confirm.

Near as I can tell, it's impossible to code out the Anti-Theft-System. The system always adds 8 back to the coding if you attempt to remove it.

Now onto my discoveries:

+00016 does something really weird... it reverses the buttons on the remote. So pressing the unlock button locks the car and pressing the lock button unlocks it. I can't see much use for that feature, but that's definitely what it does. The trunk release button still works as expected in either case.

+00128 disables the constant blinking of the alarm LED by the lock ***** of the front doors. So when you lock the doors and arm the system, those LEDs will not blink continuously. This makes sense with +00002 - Anti-Theft Confirmation via Blink. If you have +00128 and +00002 enabled at the same time, then the alarm LED will blink once when you lock the doors to confirm that the system is armed. If you DON'T have +00128 enabled, then +00002 becomes mostly meaningless because the light will be blinking as soon as you arm the system anyways. This is probably why most cars don't have +00002 enabled from the factory.

After all that, I still can't figure out what +01024 does. All I know is it was enabled on my car from the factory, and I have no clue what its purpose was. I just disabled it and will leave it that way for a while... maybe some difference will become evident eventually.

 

Looking at other Audi models, it appears that +01024 is usually Confirmation Anti-Theft Warning System Horn Activation. This is the case on B6 A4's and some (all?) A8's. So there's a very good chance that it applies to the B5 A4 as well. That would provide an explanation for every single possible coding option then. Here's a final list that's more complete than Ross-Tech's:

+00001 - Rear Lid Opening via Rear Lid Lock
+00002 - Anti-Theft Confirmation via Blink
+00004 - Selective Locking
+00008 - Anti-Theft-System
+00016 - Reverse Lock And Unlock Functions On Remote
+00032 - Locking via Speed (15mph)
+00064 - Comfort Closing via Remote Control
+00128 - Turn Off Continuous Blinking Of Alarm LED When Anti-Theft Armed
+00256 - Rear Lid Logic
+00512 - Remote Control "Close" Confirmation (1x Blink)
+01024 - Confirmation Anti-Theft Warning System Horn Activation
+02048 - Door/Window Logic (USA)
+04096 - Remote Control "Open" Confirmation (2x Blink)
+08192 - Remote Control

Just for clarification, +00032 also unlocks the doors automatically when the car is stopped and the engine is turned off.

Now... I still can't figure out why +00512 and +01024 stopped functioning on my car in recent months

I guess that concludes this single-person discussion. Thanks for your help, GoremanX! You're welcome.