Today I think I saw someone with 2017 LEL Jersey.....
Specifically on the LEL 2017 jersey, the only people I'm aware of who've currently got the jerseys to wear are members of the core organising team (PhilW had one on last year's Wild Atlantic Way, for instance), and I figure they've got a free pass.
As for other events, once you've got the jersey I think you can do what you like as long as you've got a story to tell. I'm happy to wear my LEL2013 and WAWA2016 jerseys despite finishing hors delai: I flogged on a Mille Cymru 2014 jersey because I packed after a third of the distance.
I swapped a Mile Failte 2014 jersey with another rider after PBP and am happy to wear his national audax jersey despite never having been to his country: if the situation had been reversed, I'd happily wear a jersey from an event that I'd obviously not ridden, because I could give an account of where it was from.
That said, I'm also happy to wear shorts that proclaim 'Olympic Development Team,' where the only account I can give is that they were cheap on ebay, so I'm comfortable with the idea that others may have a different view of things.