It seems like there's already the associated #c:ores_in_ground/{stone_type} tag, so it would probably make sense to cover all the bases.

In 1.20.4, where neoforge still used forge:xyz tags, there is a forge:ores_in_ground/stone_type tag. It was switched to the c variety in newer versions where nobody should be using forge: tags as neoforge now uses c: convention tags. As such, having the forge: variety (of this or any other tag) makes no sense

Which versions are supported? The tag isn't added in Forge 1.20.1

Nor is the equivalentc: tag. The data structure that generates ores is structured a bit differently then and does not have the appropriate information to add that tag, of either the c or forge variant.