Several items, for example, all the cast iron items, are missing forge tags that would provide compatibility with other mods.
For example, adding the Iron and storage block tags to Cast Iron blocks would allow them to be melted down in a Tinkers Constuct smeltery and recycled into an iron block once more.

I've noticed the same thing, and checked what exactly was missing:
-Tag forge:plates missing from createdeco:cast_iron_sheet and createdeco:zinc_sheet
-Tag forge:ingots missing from createdeco:cast_iron_ingot
-Tag forge:storage_blocks and forge:storage_blocks/cast_iron missing from createdeco:cast_iron_block