OCLP with Serial Number change breaks iServices?

So I recently picked up an older Macbook Pro at Goodwill, and thought no problem, nothing looks broken and I can OCLP to Sonoma (and maybe Sequoia eventually). The issue came when I found it locked by an organization's MDM. A little digging and I learned I could spoof a serial number with OCLP just like I do on my hackintosh, so I found a SN with an unconfirmed purchase date and set it in my config.plist.

Then, following the Doratina guide, I used GenSMBIOS to get the SN/MLB/UUID and made up a ROM. Everything booted fine and I was able to get into the computer on a fresh install, but now I get "unknown error" when trying to sign into iServices. Figured since I did the same thing I do on my hackintosh it should work, but so far no dice.

Any thoughts? Is iService just a lost cause due to the SN change?