This site has made a lot of steps forward recently in making the site easier to understand for new users and much clearer in what does what. I think the next step is to address the confusion over the "Parent Post ID" section.
I have encountered multiple newer users who don't understand what that box is for and just decide to fill it in with random numbers. Literally, that's the response they've given me when I talk to them about it. "Oh, I thought it was mandatory, so I just filled in random numbers". There's been three in the last month alone that I've found.
The problem is two-fold, I think. First, is that there's zero text on the upload page explaining what "Parent Post ID" means. Lots of the other fields on that page have a bit of explanation, PPID has nothing. And second is that it says "Ex. 12345" in the box already. This gives the false impression to inexperienced users that something NEEDS to go into that box. (In fact, a few posts by these misled users have set the parent to post #12345 )
I suggest (a) adding an explanation on the upload page as to what PPID means, (b) removing the "Ex. 12345" because it's superfluous and misleading to new users, and (c) adding an "Optional" note next to the box.