The first few sets were Galaxy foils before they switched to Cosmos foils. Maybe these Disco foils were test prints as alternatives for the second Cosmos foils. 
Also, now that we’re talking about test prints anyway: the Protostoise cards with smooth foil appear to have +15 fronts and the later Galaxy foil copy -15 (I think). 
The backs aren’t too important, since they’re MTG backs, which are (a.f.a.i.k.) always -15, since the magenta dots in some of the orbs on the back are used to determine if cards are real (e.g., the L-shape in the green dot).
Here some close-up pictures, to judge for yourself. The pictures in this first quote are taken from Travis’ video of a smooth foil copy:
And this quote is from the Galaxy foil copy, from CGC’s article:
And here also the back for two of the (smooth holo) copies from CGC’s article.
As for the holofoil of those Protostoise, they’re either smooth or Galaxy:
Greetz,
Quuador