Yeah but think of the trip to that first shot. They roll out of a Detroit factory, put on a train (I doubt covered), sit around in a yard around NYC, craned by the lifting lugs onto a freighter, possibly sitting on deck or in a hold, craned onto a pier, maybe loaded into a LST and dumped on a beach, then driven or trained across battered country-side. There's a lot of opportunity for abuse and grime well before battle.

Any recoverable US tank was repaired, the interior repainted as not to discourage the new crew, and back into action.

The Germans moved their stuff all over the place, besides the constant maintenance, etc. Imagine what a Tiger would go through with battle and travel tracks change outs, outer roadwheels, etc. just to get it to the first encounter, let alone refueling, rearming...I don't know how any sheet metal would survive long, let alone paint.

Then there's the keeping fires lit under the engine so the oil remained fluid in Russia, or using the muzzle break cover as a latrine during combat. So many possibilities...