I sent a note to the seller this morning and I already have a reply back from him this afternoon. This is what he said:
"These are NOS valves. not recently manufactured or remanufactured"
Given this reply, I would suggest that anyone buying one of those valves use it on show cars not driven much, as the old plastic just doesn't hold up well and probably won't last more than a year or two at most before failing (cracking and leaking) under normal "driver" car use. Because the cracking starts with slow leaks usually, one can drive quite a while before noticing the loss in coolant and depending on how far away you are from home when this happens, it could leave you stranded.
That is why I recommend using the metal version that I recommended to ayilar which is the Everco H1949 valve for cars that are driven frequently.