Small inconsistency, I noticed it while messing around with block tags. Cut copper stairs and their variants aren't a part of the block tag file yet, and same goes to slabs. Attached are the stairs.json files without cut copper stairs ([^stairs.json]) as well as a fixed version of the file ([^stairs.json]).

If you want to check in game if copper stairs are a part of the file or not, you can run the commands;

/tp 0 100 0

/setblock 0 100 0 minecraft:cut_copper_stairs

/execute if block 0 100 0 #minecraft:stairs

You should get the result "Test failed". Idem for slabs (slabs.json).