In the Minecraft Wiki, it says that the Fuse NBT tag on creepers contains the number of ticks before the creeper explodes. It defaults to 30s. When I allow to creeper to blow me up while in survival mode, the Fuse tag never changes. It stays at 30s. Yet when I summon a creeper with "Fuse:0s", it blows up right away. So the Fuse tag works, but it does not update naturally. I used command blocks in a repeating/chain loop like this, and made sure that the loop was active:

/scoreboard players tag @e[type=Creeper,tag=!fuse] add fuse
/scoreboard players tag @e[type=Creeper,tag=fuse] remove fuse {Fuse:30s}
/say @e[type=Creeper,tag=fuse]

I believe I am doing this completely correctly, but the chat never says anything when there is an exploding creeper.
The ignited tag is only set to 1b whenever you ignite the creeper with a flint and steel. I used the same commands as above, but changed it to use the ignited tag instead, and it worked just fine. Spammed the chat with "[@] Creeper" every time I lit a creeper with flint and steel. But this tag doesn't change when naturally blown up. And the Fuse tag never changes at all. Please fix this! It's supposed to go down by 1 every tick that the creeper is in the process exploding, but it always stays at 30s.