Loosen and retorque is the preferred method, but in this case, I did the "over the top", I felt that was more conclusive something had changed due to time only.
When I torque a head, or any assembly with a pattern of bolts, I approach final torque value by incrementally torquing the entire pattern to, for example, 80, 90, then 100% of final value. With such a procedure, one incrementally does "over the top" with each successive step. In the procedure cited in reply#5 above, the last step was simply another increment, with the second 100% value separated from the first by a time period of one month.
To accomplish my objective to observe a time factor, using the loosen and retorque method would have required me to mark the bolts relative to the head, then check angle relative to the mark after retorque. This would be impossible on all bolts except the four next to the spark plugs.
Slick