Scenario: Any blocks that were placed using older clients as stone_slab (id 44) in older servers (less than 1.12 I think) are being converted to smooth_stone_slab when the worlds are imported into newer servers. This creates a scenario where---because there's no "smooth_stone_slab" in early clients---Protocol Support renders the stone_slab (44) as a cobblestone_slab (44:3), which for us, has disrupted the feel of several maps which rely on smooth_stone_slab. Is it possible that you modify Protocol Support so that older clients interpret any smooth_stone_slab as stone_slab instead of cobblestone_slab, so they'll appear correctly for players using older clients.
This could also correct issue ProtocolSupport/ProtocolSupport#1176