Steps to reproduce:

1. Ensure you own the Halloween/Super Mario Mash-up pack
2. Create a new world with the Halloween/Super Mario Mash-up world template
3. Spawn a couple of villagers using spawn eggs
4. Now locate and go to the nearest village: /locate structure village

Observed result:
Older villagers from before the Village & Pillage update spawn when using spawn eggs, but the villagers in naturally generated villages are from the Village & Pillage update.

Expected result:
Newer villagers from the Village & Pillage update always spawn.

Notes:
This may apply to other mash-up pack world templates as well.