Other mistake: Mr. Monk is solving his 100th case, but in Season one Episode 3 Julie gives him 100 trophies, saying they rounded down from 104 to make an even number.
Mr. Monk's Other Brother - S7-E10
Other mistake: During gunfire exchange, Jack's gun locks back, indicating it is empty. He then fires 2 more shots out of an empty gun. (00:37:20)
Mr. Monk Makes the Playoffs - S7-E13
Other mistake: At the end when Bob Costas is signing off, the mic is in his right hand with the window on his right). When it switches to Natalie watching the upside down TV, the image on the screen is a flipped image (so that the mic is in his left hand and window is on his left). The broadcast wouldn't be a flipped (or mirrored) image than what we see, otherwise, everything the viewer is watching would be backwards (like the writing and numbers).