Norman - I think your memory is fine.
pr -n (lower case) was an addition early on with pr +1 or pr +2 etc also parsed. I'm going to guess that addition was either a local hack done by a lot of people or maybe on the Harvard Tape and distributed from there. It certainly worked that way in the CMU v6 and later v7. But I also remember that I had to reprogram my fingers to pr -N (capital N) when I hit other versions ??maybe AT&T Sys III??. I also remember that at CMU, tjk did not like it / was not needed because he contended we already had num(1) already on the EE systems (but not CS BTW). Ifwe had had shell aliases in those days, I might have agreed with him. But given that it was not part of v5, v6 or v7, that we only had a num(1) on the EE and Mellon systems and not generally rippled to the other CMU UNIX systems around campus, I going to take a WAG that Ted brought num(1) with him from UoMich (- which would make sense - because the BSD history says Joy wrote it). So maybe ??probably?? the origin story for num(1) is that it came to UCB from Umich when Bill and Ted were undergrads there.
FWIW: pr -n is what macOS does today.