A few I did and a few I didn't. Even the chilled ones went over some. (I didn't know that would matter though- I've been making wine for a few years and I am just starting on cider)
I watched a video where it had someone open bottles at different times of carbonation.
The ones he open early just foamed out real qucik and werent carbonated.
I would say just let it age a few more weeks and check it then.
The video is somewhere on these forums but I dont remember the name of the thread.
Extended chill periods can often help beer and cider retain their carbonation better. Store your cider in the fridge...not at room temp. Of course, you may have to store your milk and cheese in the pantry but hey...you have to have priorities.