I’m not going to pretend to have the knowledge you do, but I do know the difference between internet recovery and recovery.
I had a whole convoluted workaround to get an OS on the system at all. It came with no HDD, I had no DVDs to burn an image, and no USB 2.0 drives to create install media.
Essentially it showed up when my brother in law scored it at a yard sale. I hadn’t married yet and was about to leave town for a regular one month business trip. (Two years ago tomorrow to the day).
I was left with the few troubleshooting tools I had at her house. A 2012 MacBook Pro, Ethernet cable, and internet. I scored the HDD out of an old desktop she had in the basement.