After tonight's delivery they'll have 10 385/0s, but only 5 385/1s.
Maybe they're planning on using the 385/0s on North Berwick/Dunbar services soon. This would allow some 380s to be cascaded back to Ayrshire/Inverclyde.
Or maybe Glasgow to Cumbernauld/Falkirk Grahamston allowing DMUs to be cascaded?