I have just replaced airbags (driver and passenger) + seat-belt pre tensioners in a 2002 A3.
I used 2nd hand items given the cost of new. The drivers airbag was from a 2003 A3 (L) with a similar part number but not identical. Passenger was the same but pre tensioners on right and left were physically identical (from the outside) but had different part numbers.
I then plugged in the new airbag ECU, which I recoded and everything works fine, ie : have tested using VAG measuring blocks & can verify no shorts or open circuits exist in the airbag system. (driver/ passenger/ both left and right seat belt pre tensioners)
The above is FYI as cannot say 'all parts' are interchangeable (clearly airbag ECU modules are not) but there seems to be some margin if my example is anything to go by..
To be honest, the driver airbag deployed late and im not prepared to renew all items from VAG which would be more value than the car is worth. It's as safe now as similar aged vehicles/before the accident & that's good enough for me or anyone else.
Has anyone else had similar experience ?
Also, why are some parts identical yet have different part numbers... Food for thought..