@JayTee practically you are right. I’m sure the missing and inconsistent tables for hangers on is a mistake and the use of the table in GotU (which was specifically for the six House gangs) is the practical solution.
The reason for differences between the tables is likely down to the dates that the original gangs were published and the wording used at the time as the Book of Chaos is a copy paste of three previously published gang lists.
Personally I would prefer the rules for the number of hangers on to be tied to specific campaign rules to balance against the rest of the campaign specific rules rather than on a per gang basis. As you have noted current campaign rules include additional rules for hangers on that go over the top of each gangs specific rules but it all comes out in a bit of a mess.
Also worth mentioning that skirmish gangs do use reputation, it’s just that you are meant to agree the amount of reputation that both gangs have before the game starts on the same way you agree credit limits.