These are called paper launches lol, its got nothing to do with deliberately witholding stock. Paper launches dont have stock and that all nVidia does upon every 'release'
A paper launch would indicate there was no stock at all. You could get hold of the cards just the maket would'nt was'nt flooded with them.
Now do you remember the the Days before the Geforce 7 cards? In those days a new card from both sides would be "launched" you see reviews but then it would take MONTH for even a listing and even any stock to hit the retailers. I guess what would happen back in them days is they make a limited batch of the final silicons for reviews and the paper lunch while they go in the full production.
It was only with the Geforce GTX 7800 cards would be available on day 1 and after that most Geforce and radeon launches after then where hard ones with a couple of cases cards coming a couple of weeks after reviews which is acceptable compared to the months of waiting like before.
A modern paper launch would the the RX5500's "launch" over a month ago, no cards, no reviews , no prices, no release.