I want to share a tip I learned many years ago regarding opening tefillin parshiyos that have been exposed to heat. As you open/ unravel the parshiyos, if you hear a crackling sound, as if the letters are sticking to the back of the klaf, this is a worry. Often this is an indication that the parshiyos have been exposed to heat, such as being left in a hot car on a hot day.
The way to deal with this is as follows: Stop opening the parshiyos immediately, as you could pull parts of letters off. Instead, hold either side of the parsha and bend the parsha back and fourth for a few seconds. When you continue opening the parsha, you should no longer hear the crackling sound because the bending back and forth movement should have "unstuck" the ink somewhat. It will no longer get pulled off as easily when you open the parshiyos.