When summoning a falling block with command no.1 everything seems to work as intended, and a falling red wool block appears (time set to -9999999 in order to keep it from dying).

/summon minecraft:falling_block ~ ~ ~ {NoGravity:1b,Time:-9999999,BlockState:{Name:"minecraft:red_wool"}}

However when using the data command in order to change the Block State, the block model doesn't change even though the Block State is now changed.

/data merge entity @e[sort=nearest,limit=1,type=falling_block] {BlockState:{Name:"minecraft:blue_wool"}}

As you can see on the debug screen, there is only one entity in view, answering the question if it's possible that there are multiple floating blocks in each other.

Fixes itself when relogging