Yet you continue to discount it.
Well of course, that's where they looked. Anything found would have been in items specific to this crime. But what if they had looked in the kitchen? Would they have found PR's fibers there as well? In numbers greater or lesser than in the basement? We will never know.
Well then you aren't trying very hard because secondary transfer explains it very easily. If you want to toss secondary transfer then I think you have the burden of proving it couldn't have happened that way. (My position is that it could be either, and we have no way of knowing which)
Unfortunately that doesn't rule out secondary transfer.
And do we know how the tape fell when JR ripped it off? Do we know it didn't land on the floor picking up fibers? I don't need to resort to last minute contamination. The fibers could easily be there from secondary transfer.
http://dofs.gbi.georgia.gov/sites/dofs.gbi.georgia.gov/files/imported/vgn/images/portal/cit_1210/57/14/180852003GBI-TraceEvidence.pdf
" ... Remember that fiber matches between two individuals who share the same environment (e.g. live together or drive the same car) are essentially meaningless"
You answered your own question about primary transfer in this post. PR stated she had NEVER worn that sweater while painting, or when she had been in the basement. Never is a strong word, imho.
So, you have duct tape, found in the basement, a piece on JonBenets mouth, pulled off by JR, with FW watching. That piece of tape was torn off the roll in the basement. It had fibers from PR's jacket on it. The duct tape was not found on the kitchen counter, the junk drawer in the kitchen that the R's stated was where they kept 'their' flashlight. The roll was in the basement.
There were also fibers from said jacket in the paint tray. Remember, PR's own words, they discount the possibility of those being from secondary transfer. Just another place that PR or JR were caught showing they lied.