Purpose behind the 60% RH parameter?

UPDATE - Submitted credit and as expected was set to pending/denied with the following comments. "Please provide an hourly log of the interior RH/Temp to demonstrate compliance throughout the flush-out process". So, I set up a conf. call to discuss with GBCI and I got some additional information -- and please be gentle in quoting since I'm paraphrasing here - GBCI Response/Guidance - Project flush-out that violate the 60/60 guidelines "a couple of times" will be considered on their merit and documented corrective action. So...what we can deduce here, is that ultimately a project must provide a log of RH/temps throughout the flushout to demonstrate compliance (not surprising, since the Ref guide tells us that). What I further dug into with GBCI is that they DO agree that Mech systems provide a component of dehumidification; however, it was not provided what % that they considered reasonable. AND...it was further determined that without a log, that GBCI uses any number of local weather station (NOAA or other) archives to simply back check the potential of maintaining 60/60 conditions at a given OA rate that you are indicating to achieve flush-out. BOTTOM LINE: Keep a log. Hybrid approach with Path 1&2 was not an accepted approach if the 60/60 parameters appeared to have been violated more than "a couple of times" and there was no log to contradict weather conditions during your flush out dates. And...60/60 parameters apply to both paths.