I searched the forum on how to handle semi-detached houses having 2+ numbers and that was one of the suggested ways. Is there a more typical way to deal with this, e.g. a convention for Scotland/UK?

Scotland Land Information Service at https://scotlis.ros.gov.uk/.
From local survey I confirmed house numbers at start of each street then used ScotLIS to check e.g. the semi-detached pairs are correct.

Thanks for the feedback. It's an abandoned school, not used for anything else since. I'll fix that.

Ah, I didn't realise the imagery was off. Thanks for the correction.