Composers: From 1940 to 1958, Scott Bradley was the sole composer, not only for Tom and Jerry, but for MGM animation in general (the only exception being 1952's "The Missing Mouse", which was by Edward Plumb). Steven Konichek was the composer for the Gene Deitch shorts. Eugene Poddany, Carl Brandt, and Dean Elliott worked on the Chuck Jones shorts.
Directors: All shorts from 1940 to 1958 were directed by William Hanna and Joseph Barbera. The shorts from 1961 to 1962 were directed by Gene Deitch (and are considered to be, at best, the strangest era of Tom and Jerry, and at worst, the...worst era of T&J). The shorts from 1963 to 1967 were by Chuck Jones, Maurice Noble (co-direction), Abe Levitow, Jim Pabian, Ben Washam and Tom Ray, most of whom were alumni from Warner Bros. (specifically, Looney Tunes).
Keep Circulating the Tapes: "Casanova Cat" and "Mouse Cleaning", which may not be included in the second Golden Collection release, and weren't present on the Spotlight Collections either.
"The Mansion Cat" as well. People seem to want to brush it over, but WB made two modern T&J shorts, only one was on the Spotlight Collection, so it's a missing 3.
The Other Darrin: Spike was originally voiced by Billy Bletcher, known for his booming baritone voice. Starting with the Tom and Jerry short "Love That Pup," Spike was voiced by Daws Butler using a Jimmy Durante impersonation.
The Chuck Jones era featured voice legend Mel Blanc providing the voices of Tom and Jerry (with June Foray also providing some voice work of her own)
What Could Have Been: There were numerous stories on the drawing board that didn't make it to the screen. One cartoon, "Little Bird-Mouse" (thought up before the MGM cartoon studio closed), ended up being rewritten as a Pixie & Dixie short at Hanna & Barbera's own studio.