Intake manifold torque

About a month ago, I put the intake (edelbrock 7577) on my motor.
Yesterday, I noticed that some of the intake bolts were not tight...
I had tightened them per the FSM for 2000 dodge. With the last torque being 12ft lbs.
The only reason I can see it would happen is gasket shrinkage.
The bolts I used were just a standard hardware grade 5 with a flat washer, and oil on the threads.
Should these need to be re-torqued after a few heat cycles?
And just to clarify, its still on the engine stand if I need to change anything.
Thanks