I took it to mean that your replay star potential is refilled. If you had 4 and spent them and earned back 4 and spent 2 more you would still have 2 replays available.
If you got another boon for the following season, you could spend your 2 remaining replays and earn back as many as you have stars. If you went from a 4 star to a 5 star GM, you could spend your 5th replay and re-earn it if you GM enough games.
That would mean that a 5 star GM could have a maximum of 10 replays in a single season but that would mean that they had 5 unused replays from the previous season and re-earned them during the current season. They would start the next season with no replays and at max could re-earn and replay 5 times.