Fix updates of mounts for later dates

In !192 (merged) we deactivate the option to update mounts for a later date (originally mounted on 2020, updated offset on 2021 => two different mount settings - one for 2020, one for 2021). The functionality before !192 (merged) overwrote the mount (just 2021 with the offset then, no mount anymore for 2020).

Aim of this issue here is to re-introduce this functionality.