absolutely - there needs to be a lounge eligibility check somewhere, and that;'s the obvious and only place: they wouldn't do that check before entering the First check-in area (as Gold/GGL might still be using that area for bag drop even if they have too many guests for the full TFW and lounge) and they can't do that check after security as would (a) clog up TFW security with non-eligible passengers and (b) mean turning people back post-security

so 100% they need that lounge check there - and I guess the reason they need two separate checks, with the lounge check being "manual", is that the automated gates wouldn't cope with the guesting system (or indeed be able to make the occasional exception the staff might for an extra guest (e.g. small kids)