In short:
1. I've bought PT licenses/reinstatements on a discount before, but they're not often or regular. Been some time now.
2. An expired updade/support plan on a perpetual license can be purchased at any time in the future at no extra cost.
3. Pretty sure you're correct. In addition to my perpetual license w/supportplan, I have an expired subscription license that I expect I can revive at any time for a month or year should I want to.
It was only last year that Avid cleaned up their licensing/pricing policy and got rid of the 'fine for letting perpetual expire' and made things more convenient.
Important to remember; any license you buy thru your Avid web site account will start running immediately, whereas if you buy from a reseller, you get a code that you can activate on your account when it suits you.