The #minecraft:slabs blocks tag is missing the following blocks:

• minecraft:cut_copper_slab
• minecraft:exposed_cut_copper_slab
• minecraft:weathered_cut_copper_slab
• minecraft:oxidized_cut_copper_slab
• minecraft:waxed_cut_copper_slab
• minecraft:waxed_exposed_cut_copper_slab
• minecraft:waxed_weathered_cut_copper_slab

The #minecraft:stairs blocks tag is missing the following blocks:

• minecraft:cut_copper_stairs
• minecraft:exposed_cut_copper_stairs
• minecraft:weathered_cut_copper_stairs
• minecraft:oxidized_cut_copper_stairs
• minecraft:waxed_cut_copper_stairs
• minecraft:waxed_exposed_cut_copper_stairs
• minecraft:waxed_weathered_cut_copper_stairs

I included the current JSON files of these tags for reference.