I’m wondering whether the days of the 8-day nundinal cycle were ever named.
The Wikipedia section
https://en.wikipedia.org/wiki/Roman_calendar#Nundinal_cycle suggests not and instead the days of the Roman year were lettered A-H cyclically from the new year and
each year in a given town, the market was held on the days of a certain nundinal letter, which changed each year to preserve the 8-day cycle. I expect the days of the nundinal cycle were named locally after the town that has the market on that day of the cycle
and so no other name was needed. The nundinal letter seems to be a predecessor to the dominical letter. If so, then each year would have a nundinal letter, which I expect it was the nundinal letter of the day the market is held in the city of Rome.
I’ve read that the Dogon people have a similar 5-day cycle of unnamed market days.