Are the extras not allocated to a particular place then?
You're the regional list MP for in Scotland's case, Glasgow, so your constituency is the "Glasgow region"
So if you ran in a London borough, didn't win, but were on your parties London list, you might end up representing your voters in London anyway as a London regional MP.
It's done through a calculation and takes into consideration how many seats a party won nationwide.
If there's 325 seats available through the constituencies and Labour won 250, you'll break down vote shares at the regional level based on how properly represented Labour are.
SNP for example got 38% of the vote but won 50% of the Parliament through FPTP so they received zero regional list MPs.