Just recieved confirmation from Gazzillon that they have not yet sold 2500 Ultimate packs, which means that anyone that buys one will still get a BETA key. The exact quote is:
Thanks for contacting us regarding Marvel Heroes!
Access to the Closed Beta will be granted to the first 2,500 purchasers of the Ultimate Pack. Access will be granted within one week of purchase. Once we get close to the 2,500, we'll make sure to announce it.
Have an awesome day!
Marvel Heroes Support
So this means that the "invoice number" is not reflective of how many packs they sold (perhpas how many "Founder" packs, but not Ultimate"). So, as an Ultimate pack purchaser, I am very excited and keen to get my BETA key! I have only purchased it 6 days ago.