how to fix a clip I made too short

Stupid beginner question I hope. Early on in my projest I misplaced an edit mark and cut off and deleted about a quarter second too much of a clip. How can I, now many hundreds of edits down the road (so successive undo just isn't practical) re-edit that piece of the clip to extend it to include the missing bit?

It seems like there must be some way to select and revert that few seconds of video back to the original so I can try again. Or, alternately, a view like in revision mode in a word processor, where you can find and undo a past edit. The history window has so far proved useless, as I can't tell which of the hundreds of razor/delete operations are the one I want. Is there a way to see only the edit history of a single segment of video?

I could go back and replace the entire original clip I guess and re-edit, but my starting clips are 15-20 minutes long and have many dozens of edits made to them already, I'd hate to have to re-do that work, as it was quite fussy and time-consuming. 

Thanks for any help on this! I'm surprised it's not a common question but Google has failed me on it.