Mention repairs, decoration or building work that happened before the growth appeared, and explain what you have noticed since. Include earlier leaks, recurring wetness and products applied. Dates provide context, but a patch appearing after work does not prove the work caused it. Show the surface and its surroundings safely rather than opening a newly finished area to investigate what lies behind it.
Dust and household residue after works can be discussed through after-builders cleaning. That service has its own scope and is not a replacement for assessing mould, investigating moisture or confirming repair responsibilities.