Until a backup is verified, I’d say to never force an offline drive online. The array likely took it offline for a reason: It was failing! Unless you know exactly when it was removed, and know for a fact that zero critical files were updated after that fact, it’s just a bad idea. If a drive failed many days or months ago, all data of relevant size will be “corrupted” since the “stale epoch.” The newly updated data won’t actually be “corrupted”: a more appropriate term would be “incomplete”.
Say you have a 3 drive array and the stripe size is 64kb. Now, you force a drive that failed months ago online. Any file bigger than 192kb is virtually guaranteed to have stripes of its binary run list residing across all three drives. Any file bigger than 192kb that has been created or updated subsequent to the initial drive failure is guaranteed to be full of “holes” and essentially useless. There would be a 1/3 chance that the actual file definitions of any file created or updated since the failure would be corrupted or missing.
Often in these situations the operating system will notice these inconsistencies in the file system. It will run a “helpful” check-disk subroutine to “repair” these problems. These were not corruptions to be fixed, these were inconsistencies due to plugging a stale drive into the array. These “repairs” will permanently destroy valuable current data across all member drives, not just the “stale” one.