It seems like I’m finding opportunities to dust off my language philosophy quite often in this theory, but hey, I’ll go for it one more time.
I think trying to answer the question by providing a set of criteria creates problems that don’t really exist.
number of developers - who decides what the boundary is?
independent of a larger studio - does that mean, for example, that all games published under Double Fine Presents stop being indie games? Why, when they seem a lot like what would be described as an indie game in all other respects?
The reason for this is that there’s no real one set of criteria that counts as what we think of indie games. Nobody cooked up a set of rules for how the term was supposed to be used when it first came into usage, so it’s no use trying to apply one now.
It may be more of a case of what Wittgenstein calls ‘family resemblance’ where, for example:
game A is made with a small studio, free of publisher funding, on a relatively small budget, with a niche appeal, and it seems to be more or less what we think of as an indie game.
game B is made with a small studio, but has some publisher help, still a small budget, but it’s designed with a broad appeal.
game C is made with a bigger team, but they don’t have publisher funding, and they are making a small niche appeal game.
All of these things might reasonably be thought of someone as indie games, but they don’t all share the same traits that we might think of as typically indie. Just like how 3 people might share a family resemblance, even though individual traits might differ (A and B have father’s eyes, B and C have mother’s nose, etc etc)
So what counts as an indie game is basically any game that could reasonably be recognised as belonging to that family, and the meaning of indie is constructed by how we use it, and therefore a little fuzzy and always shifting.
Some people say indie has lost all meaning, but if that were true we’d have stopped using it - since meaning emerges from usage. So it must still mean something, even if that meaning has in reality become quite broad and vague.
Of course, this is just my own view of meaning, but I think it’s quite a defensible one.