There are basically two Mac Poor DSP&P books. One is the DSP&P, originally published in 1949 and then there is the Pictorial Supplement which was published in 1959. As I understand it, the 1976 Memorial edition is the same as the original 1949 volume. There may be some format changes. I have the 1949 edition but not the 1976 edition, so I can't compare. The 1959 Pictorial Supplement has been reprinted more recently in what looks like a lesser quality, abridged format. Again, I have the original 1959 book but not the later abridged book, so I can't compare and say anything more than that. Other than this abridged volume, I don't believe the 1959 book has been reprinted in complete form.
So, in sum, there has been two Mac Poor DSP&P books-- the original 1949 volume and the 1959 Pictorial Supplement. Any others, including the 1976 Memorial Edition are only reprints in various forms of these original two books.
Bill M.