New to BP, but I have 20 years exp in building and 25+ in managing RE facilities I have first hand exp in mitigating mold as well as DEP & EPA training.
MOLD is a 4 letter word, it is the new asbestos for insurance companies. Some legal analyst say it is worse.
Mold likes moisture + organic food and prefers similar temps to us humans. It's spore float around year round. Practically in every breath we take. It can even grow on moist metal surfaces with air passing over it. Exmple AC duct work.
The best way to control mold is to control moisture. Mold is linked to respiratory issues in young, old and immune compromised and suspected in more. Unless you live like Howard Hughes, you can only really control the moisture part of the equation.
IMO
You need to first find the water or moisture source and fix it. Your roof keeps your investment safe and dry. Do not skimp on roofing work. Just slapping on roof tar in the area is a recipe for future disaster.
As for anything suspicious, (unless you are trained and test it, you do not 100% know it is mold), mold procedures are; remove it, remediate and encapsulate. AFTER the moisture source is resolved.
So simply, if you suspect anything has mold, get rid of it. Fix the source of moisture! Dry out the moist areas. Best use a commercial drier, available at tool rental stores, then seal it.
Sounds like a lot of time and $, but the liability is major.
When installing new cellulose make sure it has mold inhibitor in it. Most now do.
There is a lot more specifics if you are interested.
