SR+ qualifies for rebate because it's a trim of the SR. The way the rules are, the base trim needs to be under $45k, but the trim you buy can be up to $55k before options and fees. So because the SR exists and is under $45k, the SR+ qualifies for the rebate because it's just a different trim level and still under $55k.
Edit: Sorry, just realized you did point out the SR+ qualifies for the rebate, but I don't understand why the old SR wouldn't qualify, unless you mean because you would have had to buy it before when there was no rebate.