In 1973, Monogram switched to a new box art design for virtually all of their existing line of aircraft kits. The light blue bordered box with a painting of the subject aircraft were replaced by an all white box with just a (rather sterile) photo of the assembled kit. One of the first new Monogram kits released with this new box art format was the P-82 Twin Mustang which included a photo of the assembled kit on a "base" (dirt as I recall). The following year, 1974, is when Monogram started including diorama construction brochures by Shep Paine with their aircraft kits. The boxes also started featuring better bases and backgrounds in the assembled kit photos on the box top. The Dornier Do335 and the P-61 Black Widow were examples of this. Curiously, the TBD Devestator didn't feature a base on the box even though it was released around the same time as the P-61. By the time 1975 rolled around, Monogram finally went back to featuring a painting of the aircraft kit subject on the box top with it's 1/48 B-17G, although smaller kits still featured a photo of the assembled kit. The reason given for switching to using photos of assembled kits was a "truth in advertising" hysteria. Revell also switched to using box top photos of assembled kits around 1973 on most, but not all, of their aircraft kits. For example, the 1973 release of the 1/144 cutaway L-1011 Tristar featured a painting of the kit while the 1/32 AV-8A Harrier, released at the same time, featured a photo of the assembled kit.
Personally, I prefer a dramatic painting to a photo of the assembled kit. I think if it wasn't for paintings on the kit box, Aurora would have gone out of business long before it eventually did ;^)
Martin