It's not an RB4 crypto, but it's still encrypted.
4Z7920930C is not crypted but some of its areas is covered with checksums or something like that. For example changing speedometer maps results with def error, but changing tachometer and fuel tank maps works ok. I have this cluster and one from late model C5 A6 which is encrypted.
From my experience easiest way to spot an encrypted Audi C5 VDO cluster is to look at the dump - it doesn't have that empty area at the 2nd half of dump, it's filled with data.
Since my engine is under rebuild process, I'm playing with Audi instrument clusters. Here's two very basic map packs I've put together for 919 and 920 clusters. Tested and works with A3 8L, A4 B5 and A6 C5 clusters. I'll update them when I find something more