Mod version: MC1.16.1-1.1.0.1

Block state variation randomness in vanilla is seeded from the block position, but updating the connected texture states seems to swap out the model being used at the positions. I expect them to remain constant. This was produced using two bookshelf models, each with their own horizontal CTM texture that by themselves remain visually identical bar the wooden frame. In the GIF it can be observed that it is alternating between the two variants during connection changes.

{
  "variants": {
    "": [
		{ "model": "minecraft:block/bookshelf" },
		{ "model": "coalescence:block/bookshelf_alt" }
	]
  }
}