Well during the closing process someone turned off the heat and knowing there were some leaks in the roof we saw that the temperature fluctuations caused the moisture in the house to expand and contract to cause our plaster to crumble whenever touched.

This is also a common solution to protect homes all over the midwest where many different issues can contribut to water penetration.  

At least in the bathrooms I can interconnect the venting with the lights to force moisture extraction.

Another issue I have is once you penetrate this skin on the foam it no longer has the vapor barrier qualities and the foam will become saturated and hold water.

I would want to dig at one or two corners down say at least 12" to see what that look like, drill a few holes, moisture test some spots inside and outside...I say go to the city and look up past permits, do they show foundation repairs, if so call up the contractors and inquire.

Source of moisture is identified and eliminated. 2.

One more thought; in my last deal negotiations I was bidding against 3 other cash buyers, my max price was 75k, but I ended up accepting the sellers counter for 80k just to beat out the other buyers, then I did a moisture inspection, found some water damage and was able to get a 10k repair estimate which I used to get the sellers to give me a 5k price reduction to 75k (I already knew there was moisture, and was already planning the rehab anyway so this was really just a bluff to get a price reduction) .

If the conditions that encourage mold to breed exist (moisture mostly) then it will come back.

Fix any moisture leaks, pest control problems, rotting.

Fix any moisture/vent problems2.