A cursory glance shows that the room type directly above King Shophouse is King Premier (52sqm) which as you said was the original upgrade they keyed in for you.

You weren't very clear about which room you got in the end, I'm assuming they didn't upgrade you and just gave you Club access in lieu of an upgrade. If this is the case then I would say that you actually got lucky, since the price difference between King Shophouse and King Premier is only $20 (from what the system is currently showing me). Club access would cost way more than that.

Glad to hear that you had a good experience at the IC SIN. I'm planning a stay there over Christmas so I'm hoping for a similarly good time.