Remember though, that Piller didn't have to be directly involved in either production for it to be a canonical dating-reference -- as a writer/executive producer on a filmic Star Trek production shot on the Paramount soundstages, if something like that makes it into an episode, it's automatically considered binding, as far as the continuity is concerned (similar to how onscreen dialogue in the VOY episode "Q2" canonically locked in the dating of Kirk's 5YM as lasting from 2265-70).Even if Piller said that, I'd still dismiss it. He wasn't involved in either the production of The Voyage Home or The Final Frontier.
The Okudas then used Piller's reference as the dating-placement of the movie in all published versions of The Official Star Trek Chronology (Piller was evidently pretty fond of referencing Star Trek V at that time, going by other nods like Wesley Crusher's great-grandfather being "a horse-thief" on Nimbus III, etc.).
Which is exactly the problem with "canon" across different series with different creators. You have people who didn't work on a production trying to interpret the intentions of people who did.
Did anyone ask Harve Bennett?
There is no way the intention between films was for a year of adventures. Why would they even reference the "Let's see what she's got" line if the intention wasn't for one following right on the heels of the other?