Having seen The last Jedi, the TIE Silencer undeniable carries some for of torp/rocket/missile. Why isn't that reflected in the game?

Could be for several reasons.

1) That fact wasn't revealed to the developers.

2) Game balance.

There's two off the top for starters.

anything that starts with "Having seen The Last Jedi..." should probably come with a spoiler warning just to prevent minor heart attacks, even if the info is very minor. The reader can't know whether what you're about to reveal is minor or huge.

Game balance can't be a reason. A missile or even a torpedo slot wouldn't break the silencer. It would just make an expensive ship even more expensive.

The reason is that FFGwasn't given any spoilery information. And even though his use of the missiles was only a minor plot point it was hidden from them.

They should just errata and say "TIE Silencer: your upgrade bar gains a missile slot"

4 hours ago, skotothalamos said:

anything that starts with "Having seen The Last Jedi..." should probably come with a spoiler warning just to prevent minor heart attacks, even if the info is very minor. The reader can't know whether what you're about to reveal is minor or huge.

Agreed!

Meh, they're expensive enough already. If you want to add a misspedo then you're probably playing casual enough where I'm not sure your opponent will care.