I've seen these reports too, but it seems to be inconsistent at best? Recently while traveling with a colleague from DEL and connecting in CDG, the DEL ground crew wrote out an invite as my guest for my colleague to be in the lounge since his ticket was business light. In CDG his boarding pass denied him entry, and he joined me as guest again. My MIL had to be guested recently in BRE since her ticket was a light fare as well, but weirdly her boarding pass had no issues in AMS. No idea what causes it to sometimes work, and not other times.