IIRC, at the time of the selldown, Duncan had over $20m in...

IIRC, at the time of the selldown, Duncan had over $20m in shares. His salary at Boss is about $1m.
So he had over 20 years salary in shares. I don't know Duncan's net worth, but relative to salary that's a lot of risk in one stock.
The board said they would not sell shares until they were in production, and they kept their word on this.
Duncan has held/bought shares for years, at some point he would want to realise a big payday.

After selling, Duncan's 25% remaining shares were worth $5m, or 5 years salary.
With the price collapse Duncan is probably down about $2m or 2 years salary.
If you were to look at a stock's insiders and see a Director owns 5 years salary in shares (well lets call it 3 years now), most would consider this ample skin in the game.

The 75% selldown was terrrible optics, absolutely.
Many anticipated some kind of nasty surprise would appear. This has not yet occurred.
The Quarterly report has been and gone with barely a whimper, everything on track as planned, no bombshells.

If you look at the broad markets, the volatility, wars in Europe and ME, yield un-inversion soon(?), global recession, there is more FUD than you can poke a stick at right now. Factor in the strength of Boss's share price at the start of the year and consider how much $$$ Duncan had tied up in one stock, then the optimistic interpretation of the selldown is less an indictment on Boss's operations and more simply just good personal wealth management by Duncan.

IMO the overall U market looks to be bottoming out now, sure we may have a little further to drop, but the risk/reward is actually looking attractive again. IMO now is the time to hold/buy. For those in the red on Boss, I personally would not be selling now, with perfect hindsight the time to sell was back when the directors selling announcement came out. If you still want U exposure, I suppose you could flip out of Boss and into another U stock but then I think any damage from the Directors selling is more or less done now, and given we've had no nasty surprise, arguably oversold.