Simosko & Tepperman show the following after the December 31, 1963 concert with Coltrane:
- Sextet of Orchestra USA session on January 10, 1964.
- TV broadcast of New York Philharmonic Young People's Concert on February 8.
- "Out to Lunch" session on February 25.
- late February: appearance at the "Once Festival" in Ann Arbor, Michigan. Plays there with a bass ensemble and with the Bob James Trio. Apparently not recorded.
- Andrew Hill Sextet session ("Point of Departure") on March 21.
- Town Hall (NYC) concert on April 4.
- Gil Evans session on April 6.
- radio broadcast with Charles Mingus Jazz Workshop on April 12 at University Aula, Oslo, Norway.
Simosko & Tepperman don't appear to indicate exactly when Dolphy joined Mingus or when the group went to Europe. Presumably that information is available elsewhere.
I found a reference to a concert at Concertgebouw, Amsterdam, The Netherlands on April 10, 1964.