And therein lies the rub. Why web covers and not promotion copies. They can pull a video off of youtube at any time, but a 45, unless they start burning books and records, I still can play and hear it anywhere. I can buy it and I can hold it, unlike a video, plus I can record it and put it back on youtube if they take it down.
You said being listenable somewhere is no criteria for commercial availability, but it is. They probably made a couple of thousand of these promo 45's and handed them out to radio stations. Now, they have value and people are buying and selling them for a profit. So now there is also a general availability to the public to buy and sell them, unlike a web cover video. And I don't know what second hand has to do with it, it is still a viable product that can be bought and sold. So I believe it fits the criteria of GENERAL availability, more so than a web cover.
I believe promotion 45 vinyls cover both criteria, COMMERCIAL release and/or GENERAL availability. Whereas web covers only apply as GENERAL availability.
So if one should exist, the other one should also be included. Or dare,I say, taken down!