My understanding is that (at least for long haul), seats are divided up with a bunch of lower cost tickets, then medium cost, then a few high cost tickets, and

My understanding is that (at least for long haul), seats are divided up with a bunch of lower cost tickets, then medium cost, then a few high cost tickets, and sold in that order. So waiting until the last 2 weeks would be a bad idea. But also perhaps my understanding is wrong / naive?