Hi Ilya,
Yes, it's possible. It's one of a workaround I thought. Then the backup data are as follows:
a. The full backup taken at least 14 days ago. b. The latest 14 days backup data
I think it would be:
a. A full backup (taken potentially months ago, exact age doesn't really matter) b. Differential #1 - diff from the full backup to the 14 days old version c. Differential #2 - diff from the 14 days old to the 13 days old version d. Differential #3 - diff from the 13 days old to the 12 days old version ...
Every day after a new differential is taken, (b) and (c) would be merged, keeping the number of differentials constant.
In this case, I concern the effect if (a) becomes too old. However, it might be a groundless fear.
I would suggest re-capturing the full backup from time to time, just as a precaution against something going wrong with a backup based on a too long series of (merged) differentials. It might be groundless concern, but then you can't be too careful when it comes to backups.
Thank you for your advice!