Bacon grease will start to polymerize at about 300° F and start to carbonize at about 375°, it’s smoke point.
On my gas stove an average empty skillet will get to about 375° on the cooking surface in about 5 minutes if on low. Hotter if left longer. On med-low it will easily get to 500°. When you add food or grease it immediately takes the skillet surface temperature down until the food gets up to the surface temperature as the food absorbs heat, then they rise together.
Often by the time you are through cooking the surface temp. is up to 500° or above - smokin’. This is why it is good to turn the temp. down after the food is warmed up. Especially with bacon. Even if you never hit 500° some of the impurities will carbonize over time.
Keep in mind the changes in temperature as you work your way above the 2,000° flame. This is just an example and will be changed by every variable. The bottom of the skillet may be 800°, the cooking surface 500°, the grease 400° and the food 250°. The bottom of the seasoning may experience the smoke point and carbonization without evidence at the surface of the oil or grease.
I think if the oil does not get hot enough to polymerize, it’s just making the pan look purdy and softening the seasoning already there.
Hilditch