Quoted from Baron_VonLoppnow:
Thanks all! The replies are really appreciated. Looking at the daisy chain diagram, it appears that I need to pay attention to W4 board. Work, Valentine's Day, life, etc. are getting in the way of looking into this right now. I'll reply again after I find time to look more deeply into this (hopefully this weekend).
(knock on wood....) I was able to make my lighting issue that I posted about a week ago disappear by disconnecting and reconnecting the data and power cables between the last functioning board #26 and the first malfunctioning board W4 in the daisy chain - I have the 7.5v boards BTW. So, for now, issue resolved. Thanks again to those who provided feedback, and a simple lesson learned to pass along. I'm now freaked out enough that unless friends are over I'll be playing with the LED brightness turned down a notch lower than "Normal".