In-universe you can always conjecture that Spock's tight-lippedness over the mating cycle is broken after he fears he killed Kirk in "Amok Time" so he no longer cares about keeping details confidential, but it is jarring how the series treats some subject one way and then one or two seasons later just regards it in a different light. I think even Leonard Nimoy complained to the producers that he didn't think Spock would be so open with an alien woman about his mating cycle but they just told him not to worry about it.