But the text says nothing about only one of them having to be in J/F; the unstated assumption, again, is that anyone on a connection is doing so on the basis of the same ticket; and, in such cases, it is unlikely that the holder of a J/F ticket would be travelling on any sector in a discount Y economy class that does not also come with its own lounge access anyway.

The "same day international Skyteam flight" is merely there to allow access on the entirety of ALL sectors on a SINGLE TICKET for those cases which otherwise would not have lounge access - domestic sectors being the obvious example - but also those cases where, for whatever reason, a mixed-class booking is necessary [though I still maintain that most J/F tickets would result in the "short" sector being booked in a similarly lounge-granting class].

Or may I suggest another scenario?

If someone flies overnight from the US to CDG on a Delta business class ticket; then relaxes for a while in the arrivals lounge at CDG before making their own way by surface to Brussels; and later the same afternoon they board a KLM flight on a separate, discount economy ticket, at BRU, transferring at AMS, all within 24 hours of having left the US on their separate business class ticket - does their Delta business class boarding pass allow them to access the lounges in BRU and AMS, too? If not, why not? a "connection" can involve a surface sector and onward travel from a different airport - so if we are to allow "self connections" this should be allowed, too?