It also starts in June here in Germany. the new PlayStation Plus, which will be merged with PlayStation Now, among other services. This will primarily benefit those who already have both subscriptions active.
The question is, how long does the upgrade last and which of the two subscriptions will it apply to, since they were certainly rarely taken out on the same day? The answer to this is provided. the official FAQ the new promotional page.
According to Sony, users benefit from PlayStation Plus Premium as long as the longest-standing subscription is active. Sony writes:
"If you subscribed to both services at the launch of the new PlayStation Plus, you will be migrated to the PlayStation Plus Premium membership plan and will have a new, unified payment date based on the longer of your two subscriptions. You will be notified by email of your new payment date and subscription fee."

Sony is showing generosity
This means that anyone who has already pre-purchased PlayStation Plus until, for example, May 2024, and also has a PlayStation Now subscription that may only run until March 2023, will still receive PlayStation Plus Premium until May 2024, at least according to the description.
However, there are also users who have purchased their PlayStation Plus subscription much further in advance, for example through discount promotions, etc., which are sometimes supposed to last until 2030. In that case, Sony would waive the actual cost of PlayStation Plus Premium, an additional €60 per year, for several years.
This doesn't seem to be a problem, as stated in the next point:
"Yes, they can keep all their prepaid time within the new service."
It's unclear whether this still applies if you extend your PlayStation Plus subscription for several more years. It seems too simplistic to expect Sony to forgo such revenue.
UpdateAccording to user reports, Sony has recently removed the option to extend a PlayStation Plus subscription for a longer period.
UpdateSony has confirmed blocking stacking to ensure a smooth transition to the new service. Naturally, Sony is justified in preventing this when it is being misused.
Once the new PlayStation Plus service is launched, pre-paid cards can be redeemed again.

Wouldn't it be simpler to first withdraw the cards from circulation and then announce the service with proper communication? Now they're generating bad PR again because they're rushing ahead without a real plan. Examples like this clearly show that Jim is overwhelmed by his leadership style. I mean, surely he must have realized this beforehand if the cards are cheaper in stores than the future pricing of the service.