It's simple. Minolta cartridges (and copies of them that were sold when Minolta 16 was in production) will work in all Minolta and Kiev 16 mm cameras. Kiev Vega cartridges are dimensionally identical to Minolta cartridges. Kiev 30, 303, etc. cartridges have a reduced takeup spool diameter to allow a longer film strip to fully advance into the takeup chamber, and will not fit in Minolta or Kiev Vega cameras.
In theory, one could modify a Minolta by replacing the advance fork with a narrower one to make that camera compatible with later Kiev cartridges, but the counters would still run out at 20 frames instead of continuing to (IIRC) 30 as the Kiev cameras do.
Source: I own multiple Minolta cameras, and one each Kiev 30 and 303.