The map
Who is under which regime, established before anybody asks what the regimes require.
Which Rules Apply Here
An organisation in six countries is under at least six sets of working time rules, and the list of which applies to whom exists nowhere.
Where the Work Is Actually Done
Working time rules generally follow the place of work, which makes a fact nobody records into the one that decides which regime applies.
The Entity That Employs Them
Which legal entity holds the employment relationship is a fact finance knows, HR half knows, and the working time register needs.
What the Contract Decides
A governing law clause settles less than people expect. Working time protections are generally territorial and do not move because a contract names another country.
Sector Regimes That Cut Across Countries
Some kinds of work carry their own hours rules in every country that has them, and the scope tests rarely match the job titles.
The Site Nobody Registered
Small offices open quietly, for good commercial reasons, and the central register learns about them from an expense report eighteen months later.
Writing the Register
One table, seven columns, one row per population. It takes a morning, it will be full of gaps, and the gaps are the useful part.