Most of us realize that the standard is that we should cite the actual source used. If our source is a derivative, we need to indicate this. I do a lot of research in archival materials. Often researchers are requested to use a preservation photocopy or microfilm rather than the original if the pages are brittle. I try to remind myself to make that notation that what I used was the preservation photocopy. (I rarely have difficulty remembering to indicate the microfilm.) Recently I used the preservation photocopy in one repository and was able to use the original because of a "problem" I found on the photocopy and needed to clarify by examining the original. It turned out that there was no difference in the two, but I needed to make sure that something had not been omitted in photocopying. The rounded page edges seen on the photocopy seemed to indicate that nothing was omitted. The sentence structure between the two pages matched, but there was a numbering issue that made me realize that it was likely the clerk had either omitted something or lost track of his numbering. Without examining the original to see if there was something inserted or in a margin, I could not be sure that the entry was complete. It would have been wrong for me to have cited the original if I'd examined only the preservation photocopy. As it was, I could actually cite both the original and the preservation photocopy.
Cite only what you have actually used. When citing personal experience, make sure it is your own and not something that has been passed down through the family. Give credit to those ancestors who shared the story with you!