A shot in the dark...

[trdcrdkid]

Besides Card Prices Update and Current Card Prices, the third monthly price guide that was around back then was Card Values Review. I'm not sure which one the OP is thinking of, because that would depend on when that last issue with the rambling letter to subscribers was. Just based on what the OP wrote, the most plausible candidate is CPU, which had the largest circulation of the three. It was forced out of business in the summer of 1984 after publisher Mark Lewis lost his longtime legal battle with Jim Beckett and Dennis Eckes, who had sued him for plagiarizing their annual price guide. I have the June 1984 issue of CPU, but not the July 1984 issue, which I think was the last one. (The court's injunction against Lewis was on July 12.) CCP, on the other hand, continued into the early 90s and then kind of petered out. I'm not sure how long CVR lasted, except that it was still around in early 1984.