Recovery tools use fact that most filesystems deletes just allocation data (data where the file is in storage) instead of deleting the whole file, as file is not allocated anymore (formally it does not exist) disk can use space that that file taken and overwrite old file.
If your tool can't recover files you searching it probably means they been complitly overwriten already and can't be recovered, and considering you recovered files from 3 months of use check if those files are partly damaged as just part of might be been overwritten (thru text files are easy to recover from such state... atleast you got part of your work safed

). The longer you wait to recover the chances for recover of clean file is lower