Essentially yes, that's correct. Your mistake is thinking that the outcome of those months of work is being able to kinda-probably fix one single bug. No: the point of all that effort is to truly fix all the bugs of that kind (or as close to "all" as is feasible), and to stop writing them in the first place.

The alternative is paradropping into an unknown system with a weird bug, messing randomly with things you don't understand until the tests turn green, and then submitting a PR and hoping you didn't just make everything even worse. It's never really knowing whether your system actually works or not. While I understand that is sometimes how it goes, doing that regularly is my nightmare.

P.S. if the manual of a library you're using is 700 pages, you're probably using the wrong library.