The IOG20 came in several variants; IOG20A, IOG20B, IOG20C, IOG20BP. There was also IOG20M.
A- the first variant (model) of IOG20 on early BYB501 (extremely rare).
B- the improved variant of IOG20A. All serial buses.
BP- is for parallel as this IOG version could terminate RP buses from BYB202 parallel buses as well as BYB501 serial buses.
C is the compact variant which has both A&B-side in the same shelf with all serial buses.
To be fair- all IOG20 could be adapted to handle parallel buses.
They were superseded by the APG40 running on a Windows platform.