First,I putted a noraml sign then write something on it

Ctrl + Picked and I put the sign with NBT on it.The block data is different from the original

I put the same sign with NBT on it and I rewrote the text.The block data like a tragedy.

I Ctrl + Picked this rewritten sign then I put the rewrote sign with NBT on it.Okay ,the rewritten texts gone.