Jeff, as you stated....application..but if you want to portray a tank with only dirt and no paint chipping..it will have to be a stateside training unit where the emphasis is on impressing the local silly-villians, full time maintenance and many daily inspections with constant washing and repainting. In a training environment, tanks are relatively recent production models and well maintained.

On overseas deployed units, most tanks have been in service many years (not new) with most of the time in the field with minimal maintenance and plenty of dings, minor field damage and spot painting with whatever shade OD (or OG) is available. Durring the post Korea, cold war-Vietnam eras we went through too many basic color changes and tanks had a dozen or more coats of various hues...just covered the glass parts with grease and spray over whats there.

Paint is generally worn off tops of grab handles, lifting eyes and hatch entrances and footprints of mud/scrapes are common on sponson boxes, bow plates and turret sides as well as oil spill areas on the engine deck and filler cap locations. Bent supports, bent/creased fenders and pioneer tools not where they are supposed to be is SOP.

The only tank I ever had that was "new" was a stateside M-41. M-47 was 2 yrs old but already had 6-8 coats of stateside paint. One M-46 was a rebuilt Pershing ...none of my 46s were maintained inside, being covered only by a 12 x 12 tarp.. and showed the wear. The average age of my M-48s was 6 years. Deployed tank units (until Iraq) rarely have clean, new vehicles.

Most modellers want to build a tank representing a tank in use with a combat unit so weathering should reflect the normal condition of the tank, taking into consideration location and weather. Stateside training tanks and museum exhibits are mostly clean with good paint. Not TO&E deployed tanks.

Forgot one tank..we tested the POS M-60 at (then) Camp Irwin, CA in 1959-60. They were all brand new with only one of 6 having a TC cupola as it had not yet been accepted.