The Americans, specifically 1CEG, used to change target letters. On my first attack at Watertown I got a score of about 30,000 feet
I didn't find out why before I loaned my offset details to Terry Lynn on 35. He got a very similar score to mine; showed the offset was good
He also had a No hats interview at Bawtry Hall with the AOC, an unheard of honour for a mere nav rad. When I met him 30 years later he still hadn't forgotten.
My next attack at Watertown was planned in detail even down to noting the target letter was to change the week we were to go. Made a good attack on the 'new' target. The bomb plot then asked us to confirm the target as we had appeared to attack a different one. Quick as a flash we confirmed we had attacked the target they suggested. We were correct; they hadn't amended their target list.