First, a BIG thanx to JJ and Carpetman. And I HEAR you, I HEAR you, and I'm thinking, I'm thinking! BUT, I'm in no hurry, and want to use the next nine months(while awaiting the return of the finished flooring to more normal moisture content level) to figure out some way to avoid having to repeat this process every year.
Next, C'man, I've covered the entire floor, wall to wall, with cardboard used for shipping large appliances, to keep dirt and debris out of the gaps. I expect this will slow the return of normal moisture content levels and the restoration of more 'normal' alignment of the finished flooring and underlayment. Not til that happens would we plan on 'doing' anything!!
JJ, this caught my attention: "Your particular installation MAY cause vertical movement if strips/planks are on-line w/a seam in the sub-floor." This is definitely the case. We made a 'story pole' and the gaps are in line with the edges of the 8" underlayment boarding. These gaps run the entire length of the floorboards, every fourth finished board or so..
You continued: "If this occurs, then shim the sub-floor from below, or re-enforce the 'spot' from below by running a support member in the OPPOSITE direction as the finished floor". It had been my thought to run boarding, from underneath the underlayment, the length of the bays created by the floor joists, and therefore, OPPOSITE(at right angles to) all the flooring as it is presently installed, and screwed through to the underside of the finished flooring, every board if necessary, or at appropriate locations otherwise. As I've said, there's no rush, but a knotty problem.
And, if shimming, where should the shim be placed in relation to the seams and/or the floor joists? What are the ‘spots’ you mention? And does it appear that I have even a glimmer of understanding what issues might be involved?
BTW, is this this the way everybody laid floors back in the twenties? And every house on the block, too ;-)