Implicit unboxing conversions

Reader Silver Sonic 1992 asked:

The Twin hammer boxes had their art changed slightly between Sonic 3 and Sonic 3 & Knuckles?

Specifically, they're referring to my dissection of Knuckles' boss area in Launch Base Zone 1, and the changes made to it between Sonic 3 and Sonic 3 & Knuckles, which I illustrated using these two screenshots:

Let's take a step back. In act 2, these boxes are present alongside each of these ascending/descending hook objects:

Here we can see these boxes are clearly using the "Sonic 3" design, even though the screenshot was obviously taken in Sonic & Knuckles. Can you understand what is going on now?

Let's go back to the Sonic and Tails act 1 boss area:

This is an instance where sprites don't use background art. The sprite-based object that Eggman carries around, which then opens up to reveal the boss, uses a different set of graphics and mappings from the solid, chunk-based boxes that are permanent fixtures of the level.

It just so happens that the 16x16 blocks along the center of those chunks got swapped vertically somehow, resulting in a weird pattern which doesn't look like it could actually open. Would've been interesting if it did, though.