The Herpstat's probe is far more accurate than any temp gun used in the reptile hobby, unless there is a huge build of of adhesive I wouldn't think that the readings are off.
does tape residue effect the accuracy of herpstat probe?
Temp guns are as mentioned not super accurate. The best I have ever seen allows double the error of a herpstat. They also are effected by reflection shiny surfaces are going to be suspect. Metals as well this includes metal oxides found in high end pigments. They are a great tool but best used for general readings and a sense of the conditions rather than critical work. I would suggest that 'accurate' is in the 1-3 degrees of an ir guns reading I would not expect better.