I have been used to Snagit saving all captures as project files, even if I edited and saved in other formats. I could always go back and find the original capture if I later needed to check or change something. How do I set Snagit for Mac to save and keep all captures?
Click on the Library button in the upper left corner of the Editor window. That will reveal the folder where all captures are saved to -- by default. You should find captures going back as far as the first day that you installed Snagit.
SactoBob is correct, one thing to note though, the Library feature is new as of version 4.0 (released summer 2016). In older versions, your old captures do exist, but they're just in a folder on disk. I don't remember of the top of my head where that is for older versions, but if you need it, I can dig it up for you.