Are newer versions of Nik Collection not backwards compatible?

I always save my Nik Collection adjustments as smart filters so that I can go back to past edits and see what I’ve done to a particular file. Today I tried to open a couple layers in an older file made with Analog Efex 2 and Color Efex 4. Photoshop doesn’t even seem to know that Nik Collection 6 is the appropriate filter set to use. It leads me to wonder if DxO has at some point abandoned backwards compatibility with new versions of the Nik Collection. I hope I’m just doing something wrong. Anyone have any experience with this? Thanks.