I have no issue with any of this ... there is an official term used by the AFL to refer to this combined record, namely "VFL/AFL", which means literally "VFL or AFL".
That’s just a poor understanding of punctuation. The slash can represent several things. You do touch on its use here though, which is to combine two expressions that are representative of one thing i.e. kitchen/dining room. This is not referring to two different rooms, one or the other, but to one room with two descriptions. Similarly with VFL/AFL premierships, they are not referring two different kinds of premierships, but one premiership prize, offered by one league, under different names. It’s a bit like referring to Brian Harris/Lake’s playing record.
Interesting to know though that you don’t have a issue with Norwood having only won 13 SANFL flags.