Lwaxana Troi was on the Enterprise-D all the time and she was in 6 out of 176 episodes.
What I'm saying is that they find loopholes to bend continuity without breaking it. They promoted Pike to fleet captain for an episode just so they could do what they wanted to do, instead of going with the most obvious implication from the dialogue in the Menagerie. It's pretty strongly implied that Spock never let himself have a relationship with Chapel before TOS because he wasn't able to let his emotional control go, but he never said it outright so the writers are free to play!