Operating below that version won't necessarily stop Ryzen from functioning as a CPU, but several notable features, most notably SMT, will be completely "broken" according to the article at Phronix.
Phronix notes that the fix landed in early February. It notes in the commit message:
After: a33d331761bc ("x86/CPU/AMD: Fix Bulldozer topology") our SMT scheduling topology for Fam17h systems is broken, because the ThreadId is included in the ApicId when SMT is enabled. So, without further decoding cpu_core_id is unique for each thread rather than the same for threads on the same core. This didn't affect systems with SMT disabled. Make cpu_core_id be what it is defined to be.So there it is, for you techno-wizards. Apparently, microcode actually is relevant to support features, and Microsoft's claims have some degree of merit.
Read the full article here by techPowerUp!