Period-value
We have some cases of periods e.g. deaths 005 and some others where the period is actually 1.january to 31.december. (because of mutations). Of course this case is for a user not relevant as the period is a year and users usually do not care for those details. However, it could be relevant at one point because of the metadata printed in the frontend and giving additional informations about the source and methodology behind (therewith expressing the period values).
It would maybe be a good use case to check whether period_value would lead to a bug somewhere - before maybe even introducing quarters, semesters and so on, which would realld lead to a meaningful change, and where actually even the train script would have to be adapted.