I know winter is the wrong time of year to be roofing, but I need to take care of this now before we get any snow accumulation. I'm in the process of laying asphalt shingles on the roof of an addition on the back of my house. After a cold snap that lasted several days, the packs of shingles that I bought froze solid. I lugged the packs inside to thaw as they were stuck together and had a tendancy to tear if I tried to get them apart. After they thawed I've noticed that the freezing may have damaged them anyway. There is a plastic strip on the back side of the shingle that has 'do not remove' printed all over it. Well, on the shingles that froze, this strip is coming off on it's own, as I remove them from the pack. I am not even sure what this strip is for- it covers a strip of tar on the back of the shingle. Can these shingles still be used, or are they now useless?