I have a box of "shame" too! Well not really shame, probably more a box of "optimism"! When I submit a design I used to order how ever many I thought I would need, but then would discover some small(or large) errors need to make changes, make the changes and scrap fairly much an entire order
I also try to sit on a finished design for about a week now before I call it mature enough to submit, just in case I forgot to add something or realized I needed to change something around. And now I always order the least amount(normally 5 or 10 panels) so at least if there was something not quite right, they can go into my junk pcb box and live there forever more without having cost too much.
Then the next challenge is to fix the mistakes without moving (or adding)any of the parts so the stencil is still usable.
I also have a text file in my manufacturing directory named "Reminders before hitting submit"
Fiducials on panel boarders and pcb's
2mm mounting holes on panel boarders
Everything on panel boarders set to "do not panelise"
Turn ratlines for gnd back on and check!
Do DRC to make sure everything is right.
Check any components that were ungrouped.
Specify laser through fids on panel boarders only.
Specify order number to be printed on top/bottom of pcb
Cheers