How can you tell if a hole has been fire stopped?

From the corridor you cannot. You see painted plasterboard and a ceiling grid.

Here is a made-up walk round, to show what to look for.

Lift a tile. Torch up. The top of the wall is open, a 15mm gap to the slab, daylight showing through from the next room. Not sealed.

Next tile. A 110mm waste pipe through the floor above, nothing round it. Not sealed.

Riser cupboard. Twenty data cables through a block wall. Mineral wool packed tight, coated grey on both faces, and a small label beside it with the product name and a date. That one is sealed.

Two bad ones to know on sight. Grey foam gone yellow and crumbly. Emulsion brushed straight over an opening, so you cannot tell what is under the paint.

Photograph each one with a tape in shot and write down where it is. Done for a whole building, that is a compartmentation survey.