But do you think they owe me for the material, since they lost it?
I seem to recall that your original post in this topic said that you would have resubmitted your material to the client, but a problem with your primary computer had resulted in your having to compose material using a second computer, and you were unable to find your material on either computer. If this content were not in your original post, then my initial reply would have been inexplicably out of context.
Being that I could be mistaken about your original post, I'll elaborate on my suggestion in a way not meant to be specific to your situation. I think it's reasonable for a client to expect a contractor to be able to resend material when necessary. I don't see how a contractor's inability to do this can be construed as the client's fault. The contractor would be advised to store material on his/her computer(s) and backup drive using the same hierarchy of folders (or directories, if one prefers that term).
Here's one way to do this. Let's denote a drive (whether a hard drive or a backup device) by "X:". The first folder under X: might be the contractor's name, such as "PERIWINKLE" (in case other people in the household might also use the device). The next folder down might be "WRITING". The next folder down might be "CLIENTS". The next folder down might be for a specific client, such as "AARDVARK_CO". An assignment from AARDVARK_CO might be placed in a folder called JOB_yymmdd (e.g., JOB_140223 if the job were received on the date that I posted this). If an additional assignment were to arrive from a particular client on the date I posted this, its folder might be called JOB_140223A. The resulting "paths" for these jobs might be X:\PERIWINKLE\WRITING\CLIENTS\AARDVARK_CO\JOB_140223 and X:\PERIWINKLE\WRITING\CLIENTS\AARDVARK_CO\JOB_140223A.
When this scheme is first adopted, the contractor could create the chain of folders X:\PERIWINKLE\WRITING\CLIENTS on each computer and on the backup device. With each new client or job, the contractor could create the appropriate folder(s) on both the primary PC and the backup device (and if extra redundancy is desired, the secondary PC). Any composed material or correspondence could also be saved on at least one PC and on the backup drive. It's also prudent to use a distinct filename for any significant revision to the material and to save that distinct filename to the backup drive, as this creates and preserves a "history."
If the need should arise to retrieve a particular document from one's PC, the above scheme should make it fairly easy to find.