The first set (also known as "press images") used to depict hand-painted resin prototypes prior to mid-2014. From wave 4 of Combiner Wars onwards, those were replaced by CG renders. Photos of prototypes are still used for redecos and re-releases of toys designed prior to Combiner Wars (such as Titans Return Cosmos, Power of the Primes Skrapnel or the Platinum Edition Autobot Heroes set).
The second set usually depicts (near) final pre-production samples, typically including photos of the tos inside their packaging.
However, there apparently used to be no communication between whoever was responsible for each of the sets, so the figures would typically be depicted in very different poses, and the alternate modes would sometimes face opposite directions. Mistransformations could happen in both sets, but usually you wouldn't see the same mistransformation in both sets. The CG renders don't include actual mistransformations for the most part (although PotP Hun-Gurrr is missing his head in some renders depicted on his packaging).
Starting with Power of the Primes and Studio Series, though, I've noticed that the second set often tries to mimick the poses from the early CG renders, with various degrees of accuracy.
Here are some examples:
Edited by Nevermore, 23 April 2018 - 03:16 PM.