The sadder thing is that Eliezer doesn't seem particularly bothered with numbers either.

I beg your pardon. Check Ch. 30 and you should see some non-canonical first-year student cameos in Draco's army. For, may I mention, exactly that reason - I was explicitly familiar with the dilemma of the discordant Rowling statements and decided to resolve in favor of Hogwarts having around a thousand students, so that having around half the students sign up for the armies would give you 72 first-year soldiers.