What are some non correctable analog capture issues?
 

Just wondering...there seem to be a lot of improvements we can make to raw footage but what are some issues that have yet, or may never, found to be fixable?

Software timebase correction doesn't exist. Many have tried, some have even come close, but all have failed. I've worked closely with a few video filter developers on this, providing them with some tricky footage.

You usually can't fix serious tape errors -- garbled signals, tracking errors, etc.

Trying to restore nth generation copies of copies is one of the harder VHS restorations there is. And it all starts with the capture quality. This is why it's important to have specialty hardware for various errors.