Help!/The line on out-of-universe source validity.

I've been pondering over attempting to rework some of the page for The Dark Dimension, as well as the production page for 1990 in relation to the plans had for this story over the course of the year.

However, some of the dates for key points in the preproduction plans of this unproduced story seem to only be present in Josh Snares' mini-documentary on the matter (Offsite linking obviously not allowed but it's under Doctor Who: Oddity if anyone wishes to seek it out) and T:UNOFF REF is, of course, about tackling such things case by case.

The thing about the mini-doc in question is it doesn't feature interviews with any contemporary figures involved, and insightful as Josh is, he doesn't have a citation list featured or attached to it.

As a newbie to interpreting the more nuanced policies of the Wiki like this, what would be the best approach for this one?