There are zero differences in towbars for cars from SOP - start of production in August 1999 - to EOP - end of production in May 2005, none. The shell remains the same, only the 3L is different and the wiring is different depending on whether you have DIS or not and therefore bulb checking. I don't understand why suddenly Rameder is showing two different products for the early vs the late cars; this never used to be the case but I suspect it has to do with the really early cars actually not being homologated for towing. Getting a replacement sticker is a trivial affair, I've heard of it being completed quite a few times.
There were two producers of towbars during the lifetime of the A2; AL-KO produced the factory gear (which is what I have in the garage awaiting time) and GDW produce the aftermarket bar. There's a variation I've seen once out of Poland but couldn't find again.
Both use exactly the same setup with the holes in the shell, the two small plastic pieces to hold the end of the bars in place, even down to the massive 6mm pop rivets to hold those pieces in place.
Wiring only differs if you have check control for bulb out in the car or not. There's no coding to be done, either. The only good loom is from Erich Jäger.
Originally it would appear that Audi never intended the A2 to be a towcar, or more to the point, they didn't get that testing completed in time and so the early cars may not have the correct approvals in place. Since you're in the UK, you won't have to go and get the 'bar MoT'd, so you should be good to go anyway,
if there's a towing weight in your v5 documents. Please check that. The 1000kg is a weight given online, but check the documents before your insurance company does it for you.
Here is another link to Rameder (one of the biggest towbar joints in Germany):
https://www.rameder.eu/gdw-towbar-detachable-towball-inserted-from-below-165687-04382-1.html, specifically for the early A2.
Remember that your nose weight cannot exceed 50kg! The D-value is also really low at 6.1kN, which is not enough for many bike carriers. You will likely get a 13pin electrical setup.
- Bret