It’s the fixlet inspector. It can’t be evaluated in the context of a fixlet relevance.
I found this is in the fixlet inspector docs , where it says “these inspectors only work in the context of property evaluation, not fixlet evaluation”
I have found that it does work in an action script. So an approach could use action script which would do something when there’s no more relevant baselines.
// Action script
if {not exists relevant fixlet whose (exists header whose (name of it ="X-Fixlet-Type" and value of it = "Baseline") of it) of site whose (name of it is "Catch-Up Site")
}
// do something