Dark patch on floorboards

[zowie]

We was changing a toilet but now we have a few patches on the under side of the floorboards upstairs we have checked the toilet and even put tissue under everything to check but definitely no leaks anywhere but when we pulled down our ceiling under the toilet room the floor boards look damp we are stuck to what it could be as nothing is leaking any advice would be great

 

[blup]

A historic leak; water might have come out when you changed the toilet over; over the years an intermittent dripping can soak a floorboard - all or some of these are possibilities.

Blup