In the meantime, from the App Store I'm downloading 10.9, 10.10, and most importantly 10.11 (for my MacBookPro5,5), just to keep. I already have a drive full of clean install partitions for everything from 10.4 to 10.13, but didn't actually have the original installer images for all of them. Or actually I did, but storing them natively on my NAS with ext4 file format causes problems. This time I'll package them in a dmg file for storage.
Since I couldn't download the old OSes on my 10.13 MacBookPro5,5, and since I can run them on my 10.7.5 MacBook either, I put the 10.7.5 MacBook into target mode and booted 10.7.5 from my MacBook Pro. Then I initiated all three downloads. Actually, I don't know if that was even necessary, but it only took me an extra 2 minutes to initiate so no biggie. Is it possible to download 10.9-10.11 on a machine that is limited to 10.7, if they're already listed on the App Store as a purchased item for me?