While using the selector tag to edit the nbt data of some blocks (EX:Text1 in signs) everything will work correctly, but when trying to use selector to change other nbt tags (EX: Command in command blocks) it will not work and will simply display the string.

EX:

/setblock ~ ~ ~ wall_sign 0 replace {Text1:"{selector:\"@e[score_A_min=1,score_A=1]\"}"}

works correctly and places a sign displaying the name of the entity @e[score_A_min=1,score_A=1], but

/setblock ~ ~ ~ command_block 0 replace {Command:"{selector:\"@e[score_A_min=1,score_A=1]\"}"}

places a command block with the command

inside, instead of the name of @e[score_A_min=1,score_A=1].

Tested a bit more and selector won't work with summon either.