I take it the only factors listed there are those that haven't had any PRP test done, i.e. those that were found for a k whose upper bound was slightly lower than the maximal upper bound of any k?
Correct. And this is the slightly depressing list, because so far all those that have appeared and then disapeared have done so because PRP tests have been returned. We have yet to have one make it down to the 'n upper bound', although I think we are reasonably confident that Xrillo's and Xeltrix's should make it.