I've often made models showing repaired damage, especially if I can find photos of it or historical records of what damage was inflicted in a battle.
For instance, I've done tanks with scars of richochets on the mantlet, a bent front fender over one of the tracks, rust and smoke damage around the exhaust and of course, dried caked-on mud on all the lower surfaces. Maybe also paint worn off where boots would scrape while climbing into the turret. Aircraft with small patches over bullet holes, maybe the paint there a little brighter because it's newer.
At one time, I was planning to do a diorama of the Battle of the the River Platte. I'd just read a book that detailed where each shell hit and what the damage was. There were kits available of Exeter, Achilles and Graff Spee, all in the same scale and Ajax was a sister ship of Achilles, so that was doable too. I just never did it.
Since the city just next to where I live is Ajax (there are lots of ships named after cities, but Ajax is the only city named after a ship - all the original streets were named after crewmen), maybe one day I should build it.
Anyway, back to the U-boats. It makes snese that if you know a boat has had some mods (like the CT being modified from Turm 2-Turm 4), that the newer sections wouldn't be as weathered as the original.
I often try to make differential weathering on my decks. More where people walk a lot (around hatches and guns)), and less where they don't.
