I was taught https://en.m.wikipedia.org/wiki/D%27Nealian

The uppercase t and h are the two main differences, but I guess I adopted the spencerian or copperplate version at some point.

Lampblack ink or india ink was in use as well and spots with lots of pigment can have it move when wet.

Edit: it would seem synthetic aniline based black inks were in use for personal writing by that time. Aniline black isn't even close to waterfast, so that might very well be it.

Ah, I didn't know about aniline-based inks being used with dip pens back then. Thank you for that nugget of information!