wmc83, that's not how I read it. Looks like a yes to me.
That said, the vintage 'movement' has until recently been Pre 85 only. However as from this year, the MoMS has included Pre 90 for both MX and Dirt Track. On that basis, although it is up to event organisers, it seems reasonable to extend Vinduro to include Pre 90. That would make your 89 RMX perfectly acceptable.
Now personally I disagree with including Pre 90 in any definition of vintage, but there it is. And no, I'm not trying to derail this thread so let's steer clear of that can of worms. All I am saying is that it seems based on what has happened for vintage MX and DT, vinduro should reasonably be extended to Pre 90. It should at least result in more bums on seats!