The image below is what I see when I view both the website & the Viveport app, there's no mention of "While Supplies Last" anywhere in that image.
All that's stated is that it's a "Limited Time Offer", which would mean that the deals are available for the duration of the sale (time period, NOT quantities).
Reading lines like "We hope you all enjoy the excellent titles you’ve picked up" when the marketing team can't even fill the demand is laughable.
It even comes off as a bit cocky, mocking those who may have made the effort to check out the sale, only to not be able to buy what was advertised.
There are still a couple of days left during what was still just a very short sale, so it's not too late for them to do the right thing and perhaps do a refresh on the offers.
Or not...but it's just another nail in the coffin for HTC's already questionable customer service reputation.