I'm confident that QRecall will know when QRecall archive data has been corrupted and I understand that QRecall doesn't need the original to do this. If I think that one of my originals has become corrupted, and I haven't modified it since the last capture, I can recall a copy from the archive and then compare it to the original. However, if one of my originals has become corrupted and I don't realize it, the corrupted file will be captured into the QRecall archive the next time I do a backup. As old layers are merged, the uncorrupted file will eventually be gone from the archive. I'd have some time to recall the uncorrupted file from the archive, but I'd still have to realize that the original was corrupted. If QRecall knew that an original has changed, but it shouldn't have since the last capture (because the modification date of the original is the same as the one in the archive), then QRecall could alert the user that the original may be corrupted.
James Bucanek wrote:Applications do not update the creation, modification, attributes, or access time of file objects. That's handled automatically by the filesystem. In fact, an application would have to go to extraordinary measures to modify a file in a way that made it appear that it hadn't. I'm not aware of any apps that do this.
The only instance I can remember where this happens is with AppleScript Editor in Snow Leopard when modifying scripts saved as applications. The date modified of the application didn't change when I modified it with AppleScript Editor in Snow Leopard. However, a few minutes ago I opened a script I hadn't touched since 2011 by using "Show Package Contents" in the Finder and items inside did have modification dates that were later than the application's modification date (which, in Snow Leopard, always stayed the same as the date created). So, the files that I modified apparently did have updated modification dates but the package/application containing them did not. Apple seems to have fixed this in Lion or Mountain Lion: scripts saved as applications get updated modification dates when they are modified by AppleScript Editor in Mountain Lion.