My Gritti Palace SNA come through as confirmed on my migrated SPG reservation. I cancelled and re-applied the SNAs last week to try and minimise my chances of issues.
The reservation remains visible on Marriott.com and shows the upgraded room. I have saved a PDF of the updated reservation in case of any issues.
Am I 'out of the woods' here, based on the problems others have had with migrated reservations? If not, what should I be watching for?