I found similar issue when I tried to redeem Pluralsight course offer from my company's MSDN subscription. I could only choose from a limited number of courses, most of which I was not interested in.
I think the key wording in the offer is "up to 30...".That implies to me that it may not actually be 30, in a given case.
You could try contacting Pluralsight directly about it.
Good luck,
Phil Streiff, MCDBA, MCITP, MCSA