From what I've been able to gather over the last few years, is that there's a lot of variables to whether or not any show will do this. How many industry invitees end up accepting, what the producers/other powers that be decide, etc. I saw Pretty Woman had plenty of seats left for their official opening, which honestly doesn't give me confidence about it's future, but that's another discussion.
Potter did this via the TodayTix lottery, which honestly shocked me, I didn't think there'd be any seats left at all considering the amount of industry that I'm sure was invited to it. Frozen def had their opening blocked off/unlisted in Ticketmaster, but I never checked back about that. Of course, it also depends on the popularity of the show at hand. Obviously with a Disney musical, there's much less likelihood of any public attendance snagging tickets to opening than there would be to say, the recent revival of "some play that the general public has never heard of". Just to clarify, that is NOT a knock on any show at all, I'm just trying to get a point across.