They're both exclusive to the box set though Elite released a nice Inseminoid disc. I have that in my R1 British Horror box set and a corker of a set it is too.
Why don't you want the whole NJW set? I love Satan's Slave and Terror and the 5th disc with Warren's rare short film 'Fragment' and extras is priceless. Rarely do special features come across as so enthusiastic and personal to the guy its about. It's a stunner, Vips. I recommend you add it to your collection at once.
When I think of all the cool stuff Anchor Bay released it makes me feel sad. I want them back!