I think the term "We're not hardened Swingers" generally means they have a life away from swinging and don't necessarily live, eat and breath swinging. We might all term the level differently I am guessing so best to find out from the people themselves how often and active they are.
Yeah a bit difficult to really define what 'hardened swinger' really means. I guess along with what Minx said we'd add that it would be people who would jump on us and do or try and do really pervy stuff that we weren't prepared for. Along with possibly having a really overly spacious and loose vagina leering at you with a contemptuous smile from between a set of leathery inner thighs or a cock with bite mark scarring and adorned with tattooed notches along the shaft.
IMHO swinging is a part of my life, whereas a hardened swinger is someone for whom swinging is their life.
However I think many people refer to hardened swingers to reflect someone who has a experienced several meets.
Several is defined as: More than two but not many.
Makes you wonder how many is many, well it did for me?
Well apparently many is defined as: Being one of a large indefinite number.
So several is somewhere between three and a large indefinite number.