1. [untitled], April 8, 1968. Fifteen unclued lights go with five theme words. Easy. The editors printed it under the title "New York Magazine Puzzle," aptly enough.
2. Dedicated Dodecahedron, April 15, 1968. A dodecahedron-shaped grid where each face was a five-letter word sharing its letters with a six letter word. Very easy as long as you can figure out the person to whom the puzzle was dedicated.
3. 3 Downs, April 22, 1968. 24 of the clues are anagrams of two words rather than the standard definition/wordplay construction. You have to use those words to determine a third word to go into the grid. Moderate difficulty: I recognized a few of the pairs which might not be familiar to younger people, and that helped a lot.
4. One Shy, April 29, 1968. A straight bar cryptic, with a hidden message you have to find and interpret. Easy.
5. Diametricode, May 6, 1968. I remember solving another of this type--might have been a Maltby. Fifteen of the answers must be enciphered before going in the grid, with the substitutions shown by the letters extending out from the grid. Hard.
6. Woodbabes, May 13, 1968. 24 of the lights are what I call visual puns, where the physical placement of the letters is indicated by the answer phrase. So if the clue led to "babe in the woods" the light would be "woodbabes." Sondheim gave enumerations for the lights, not the answers, which made this very hard.
And you thought that the term "snail mail" started with internet-era hipsters looking down on their old-fashioned elders? Think again.