Lessons learned

Always check which version you are using.

I was oblivious to the fact that I was using gnuplot 5, not 4.x - banging my head into the wall for a couple of hours. I was not using gnuplot directly, so I might be excused? Right? …

The epslatex terminal with dashed lines had been deprecated since I used it last time. Googling did not result in up to date documentation, since the manual is only published as pdf…

For future reference: dt is used for dash type… and the manual was here.