Originally Posted by
Bat-Meal
Well I haven't read it yet, but the 'We Are Robin' series had a hole bunch of unofficial Robins running around at once, didn't it? Which I think, in combination with the number of past official Robins, has turned the mantle from what was originally a character, and then a term for a Batman apprentice - potentially into a term for a Gotham vigilante in training. Or that's how it seems to me.
I only know of official Batgirls so far, and cannon-wise Babs is the only one since Cass and Steph's time was retconned for now. It's also gender specific, but if there were multiples I'd say it would still mean: Batman's (female) Apprentice.
As for multiple Batwomen, it starts to get tricky because it isn't an apprentice role and assumes a certain level of competence and independence. At a guess the title would mean: a bunch of adult women operating as vigilantes in Gotham, possibly all wearing wigs.
This is my interpretation of what the mantles could then mean:
Robin = a Gotham vigilante in training
Batgirl = Batman's (female) Apprentice/s
Batwoman = an adult woman operating as a vigilante in Gotham
Which is indeed a dilution, and no longer a specific character per say.