I'm slightly confused by this post. Is there any circumstance under which a non-EU/non-Schengen visa/passport holder cannot visit a FCL if going non-Schengen to non-Schengen? My father is travelling DEL-FRA-EZE in F with a 15 hr layover and I would be really really angry if he had to spend this time in a SEN or C lounge. I booked him specially in F so that the FCL would make the long layover bearable.

If he arrives or departs from B non-schengen then obviously he has no problem (whether the security ppl will let him into B 15 hrs before, when his flight has no gate, could pose a potential problem).