It's not a can of worms: In Sweden we use spaces to separate groups of thousands, and the decimal separator is a comma. 2 500,50 while the Americans, among others, use commas to separate thousands and full stop as the decimal separator: 2,500.50. Sadly, I have come across problems now and again because of (old) software that only recognises the American separators!Interesting question.
Actual usage is, as you have noticed, all over the place.
Normally, such large numbers your probably be written with digits only (which opens the entirely separate worm can of what to use as a thousands separator!).
That document is a life saver, thank you for uploading it! I have my own queries from time to time but I'm too stingy to actually buy those kinds of books!This document (section 9.1.2) (aimed at public management) notices that large numbers are sometimes written out as a measure against forgery, and gives an all-joined-up example without comment.
Once you go above a million, I would personally split it like "en miljon fyrahundratrettiotvå tusen femhundranitton", simply because its gets unmanageable without the spaces, but I rarely write cheques for that much (or any cheques at all, for that matter...).