I understand. And that's exactly how I did it. The reason I knew it was in Part 3 is that AFTER it failed after I unrar-ed in Part 1 ONLY... I checked which part it was WITHOUT un-rar-ing it to find out if the error file was in 1 specific rar (did it crash while extracting 1... or 2... or 3... or 4... and the name of the file in which it crashed... is rar #3)
Said another way, as you said, all 4 rars are in the same folder, I extracted just Part 1, and it has an error when 7zip was extracting the files in Part 3... every time... never getting to Part 4. Downloading Part 3 from different mirrors... don't help. And yes... it's the updated 7 zip (19).
Thanks for your help though. It's appreciated.