jr-pass old price, new rules?

We have a question concerning the jr-pass and its price increase with accompanying change of rules. simply put:

We will be arriving in JP right after the price increase. We have to buy the pass before the price increase, but activate it after. Will the pass be accepted with the old price? Will the new rules (allowed on Nozomi and Mizuho shinkansen) apply for us?

I have tried in several ways to contact JR, they dont respond (at all). Any educated guesses from this forum?

You cant board Nozomi and mizuho trains with old JR nation wide pass.If u buy JR pass on 30 sep 2023,you can activate pass within 3 month.you dont need to pay newprice even you ride JR trains on 30 Dec with old JR pass

So your guess is that after oct-1 all passes will allow all trains, even when the voucher was bought before oct-1? As long as the voucher is redeemed after oct-1 we should be set?

Using the term "old" JRP is a bit of a misnomer given the current pass versions have been around for three years (I've used several that I am eligible for), just that a lot of people have not visited recently so still think the retirement of the old booklet style is a recent thing.
For the change in "rules", what the rules in place at the time of use will dictate which trains you can use, not the date of the purchase of your pass. So, buying at one price and one set of rules pre the change will not limit the usage of the pass when used after the "new" rules come into play later this year.
Logically, it would be a huge mess if the date of purchase for the national pass made a difference with tens of thousands of different combinations making it almost impossible for JR staff to efficiently process tickets.
As a subsequent note, not all the "rules" have been announced and as I understand, the actual/precise date of the change isn't set.

when they use the common sense in Japan,
the old voucher can be exchanged to the old pass and the new voucher can be exchanged to the new pass.
the old pass is used under the old rule and the new pass is used under the new rule.
otherwise, the treatments are unfair.