Sets with real variations.
1. Model 493 (us-version of 926):
The first edition of this set came with a flat baseplate with craters being build from standard lego pieces. Later sets came with a classic craterplate.
2. Model 6851:
There are two different types of chassis to this set.
3. Model 6923:
Look at the rotor and the loading crane. They are different.
4. Model 6987:
This set came with two different types of fixtures for the large sidewalls.
The later version of the building instructions has an additonal inlay on one building step. In the first edition there has been an additional black and white sheet showing this difference.