Yeah, the number schema for AMDs motherboard Firmware called AGESA, can be a little confusing. AGESA is the basic firmware provided to motherboard manufacturers for them to work with and entails memory and CPU support etc.

Currently we are ar AGESA revision 1.0.0.5 whilst some motherboard manufacturers are still at 1.0.0.4B and then there's AB ABA etc. Upcoming motherboards based on the B550 chipset are expected in mid-June, and afterward another update as the desktop versions of the Renoir APUs are also on the horizon. Rumored as well is the Matisse refresh (XT).  So there's a lot of BIOS changes. That said, over at Hardwareluxx one of their community members noticed this when checking firmwares:

ComboAM4 1.0.0.4B does not follow 1.0.0.5, but ComboAM4 v2 1.0.0.0. The numbering has restarted and a small "v2" makes the subtle difference clear. Why there is a restart in the numbering is taking place is not really clear. An MSI MAG B550 Tomahawk revealed AGESA version ComboAM4v2 1.0.0.0, while a Gigabyte B550 Aorus Master apparently already uses the ComboAM4v2 1.0.0.1 version. It's getting rather confusing really. Perhaps V2 entails to 32MB BIOSes.

AMD B550 Motherboards to Get AGESA numbering refresh, with v2 Suffix