Thanks for the replies so far ... just like A3 customer service, I'm getting different answers from different people to the same question!
Here's the bit that gives me hope from M+B website ...
To upgrade from Silver to the Gold Tier, all you need to do is fly Aegean or Olympic Air at least four times and earn 24,000 Tier Miles within 12 months or collect a total 48,000 Tier Miles, regardless of which airline you choose to fly with. Whichever you do first will get you there.
To retain your Gold Tier, you have a fixed 12-month period from the date of your upgrade or renewal of your tier to collect 12,000 Tier Miles, including 4 flights with Aegean and/or Olympic Air, or collect a total of 24,000 Tier Miles, regardless of which airline you choose to fly with.
That seems to be making a rolling / fixed distinction between qual & renew. I'll be silver the whole time, and earn 24k + 4 within 3 months while silver. It's just the silver requal date is in the middle of that 3 months.
The bit that causes doubt is that my gold qual by date and silver renew by date are only a day apart. That could be because my miles for gold will reset (1 month after flying) or because my last activity that counts towards gold was on that date.
Sadly me wanting something to be true doesn't make it true so I guess I'll have to wait and see.