Uhh, lets go with 3 for 4 people total. Collar's have nothing to do with it. Girlfriend, boyfriend is just a verbal agreement. If you try to escape the prospect that it's not a harem because you haven't verbally agreed on declaring someone a girlfriend then you are just being dumb. What is really the difference between a distant girlfriend and a clingy friend with benefits? The difference is being a girlfriend doesn't fucking matter, you are still not involved in the harem so you are not part of it.How many girls are required to count as a harem?
And as of the current version he's only collared three girls, though I admit it's clearly not going to stop there.
I dunno, don't fight me, I don't entirely trust my own words here. There's probably some semi agreed on rule for all this, somewhere.