I may have found something on that Copyright Records website about which you told me:
I bolded the salient text.
So I am guessing The New Mutants was delayed (but already had the cover printed), and Marvel decided to print off a small portion of Canadian price covers instead of trashing a bunch of single-price covers.
All very interesting. (thumbs u Anecdotally, the run of MGNs from one of the collections I bought starts at #5, and there is no #4.
And, one of my #5's is a later print . . . (still a sweet copy, though)