When declaring model overrides in a model that inherits quads from a parent, the overrides are not applied, as CTM does not process the parent quads and their tint indices during the stage that the overrides are applied to the model. An example model for producing this bug can be seen below.

Mod version: MC1.12.2-0.3.1.16
Forge version: 1.12.2-14.23.4.2705

{
  "parent": "minecraft:block/grass_normal",
  "ctm_version": 1,
  "ctm_overrides": {
    "0": {
      "type": "normal",
      "extra": {
        "light": 15
      }
    }
  }
}

This may have been fixed by b2cb2fd

Worth a test.

Not quite, it will only work if the parent is also a CTM model, not with vanilla models. However that's likely as good as it's going to get within 1.12.

Upon further review, no this doesn't fix the problem at all. This was to fix an issue when combining texture and model metadata, not with model inheritance. Ah well.

Issue #144 is related if not a duplicate.