This is all beginning to remind me of dealing with CSS
Other peoples' badly-written CSS, that is...
You end up writing ever more fiddly, stupid and idiotic clauses & conditions to catch ever more niche cases and the entire thing becomes an utterly farcical and unworkable pile of unfit-for-purpose shit.
All because someone doesn't wan't to sit down and re-draft the lot sensibly.
This is now how I think of HMRC.