90 boosts still available.

So as you all know they've been replaced with the 100 boost, but I'm hear to tell you,

The 90 boost that came with warlords of draenor can be applied and added to accounts multiple times in any amount on the same license.

If you're lucky enough to find the old warlords of draenor cd keys on a website or bought them before. 

If they remain unredeemed you'll be able to do so multiple times, different keys each time but as many keys as you like.