I have been in dialogue with Wargaming support about this - the premium discounts they mention should be in the Epic store (so the one on the Epic games launcher) and not the in-game premium shop.
When I pointed out that the Epic Games launcher just states that World of Warships was coming soon, despite the fact that I have gone through the pain of downloading and then setting up a new account to test for them, support shrugged their shoulders and said nothing we can do and no 'up to 80%' discount on doubloons until Epic decide to implement it. This was a big incentive for me this morning given that the in-game chain of missions to get an Epic Games supercontainer would take quite some time to do given they are sequential missions and I would rather spend that time grinding my main account ships rather than starting from Tier 1 ships again.
Unfortunately, as a long time player of WOT and more recently WOWs, this is the kind of response I have come to expect from Wargaming, but I am now extremely unlikely to help them next time they ask for it.
A sensible way of rewarding testers might be for them to offer the doubloon discount offers via a coupon or similar on our main accounts (given that the e-mail said the purchases would be mirrored anyway)