Also Eko and Bernard never have meet with orginal main cast but they was in same airport and on same plane that it's possible that they have to see few characters . Because Bernard seat next to Jack and it's possible that Bernard have see him.
The Man in Black was only main character who born on the island and afters 2000 years he meet with orginal main characters when they appear on the island because he never left the island.
Penny was only main character who meet with orginal main characters after the island because she never was on the island.
Libby was only main character who have saw orginal main cast before the island but don't speak with him . Same thinks it's possible happen with Eko and Bernard possible that they have see orginal main cast but never speak with him or them.
Desmond was only main character who meet orginal cast member 3 years before crash . Same think with Charlotte it's possible that she have meet or see orginal main characters 30 years before crash when they was traveling in time and stuck in 1974-1977.
So it's mean that Juliet was only main character who never actually have meet with orginal main characters off the island or in time travel.