missing files

Hi all,I am new to logic so any help will be much appreciated.My question is this...I am working on a project of 10 compositions at the end of a work session I 'save' into a music folder I have created and also a 'sve as' to an external hard drive.In no time at all my files were getting larger and larger with all of the various versions.To free up some storage space on my Mac I started deleting the oldest versions of those songs.Then suddenly when trying to open a composition I started getting the 'file not found in its expected location.The first time it happened I 'skipped all' only to get various empty regions.I then closed down and reopened using 'search' expecting it to find the various files...it didn't I had lost a couple of days work because i had deleted older versions.Does logic require you to save all of the previous saved files in order to enable it to open a most recent version.surely this isn't the case.As already said any help on this would be more than appreciated.