Hole diameters and slots are always expressed in finished size, the board house choses a proper drill size to account for plating etc.

https://www.cogra.se/

Milling tolerance: 0.2 mm (Implies board edge clearance > 0.2mm)

Plated slots: size >= 0.5 mm, length >= 2*size

http://www.magazines007.com/pdf/PCB-Mar2017.pdf

Openings in solder mask smaller ⇐ 0.4 mm is difficult