While Bizon was a nickname for the VIRM, it lost that name quite quickly after the first presentation. The formal name (that has been scrapped because the system the name was based on was never implemented) was Regiorunner. It also has this name in v1 of the set.
#3 Updated by foobar about 6 years ago
which you missed to include
They're in r311 and r312 respectively. The nightly compiled while I was in the middle of those.
I just messed up the names there (too much copy/paste). There never existed a VIRM-III. The current VIRM-IV is also the IRM-IV, with properties updated in 2002.
But IIRC the name 'bizon' was used longer than 'regiorunner', which is why I went with that. Plus it nicely matches the animal names of other trains