If care has been used to remove and replace the screws then it would lead me to believe, that care was used while working on the inside.
Many guns that I open with chewed up screws, show signs that Buba
did just as good on the inside with his 1 screwdriver and hammer that he had in his tool box.
A person with proper tools and experience can work on a gun, and leave no evidence that any work has been done.