P:(Masking) Show masks started outside of subsequently cropped area

Actually, I don't even need to zoom out (or at least not further than fit).

If I press K, I can see my outside-of-crop mask markers on the edges (similar to my first request).

I just didn't see them before though I mostly catch up my markers in fit view.

I'll keep an eye on it for the next few days and then mark it as resolved if I find them reliably there.

Bingo @GoldingD 

 Zoom out

Yes indeed, creating a virtual copy and destroying the crop in the copy, editing the masks, before copying it the crop adjustement from the previous copy is also a possible workaround!

I use copy/paste adjustments regularly, however rarely for this. 
Depending on how I feel, I can also create another mask within the crop area and set new adjustments from it. 
That also works, unless the previous mask is very precise. 

Just a thought, create a virtual copy, then move on to your additional tasks.