In my post on the Merl Saunders and Friends gig at the Inn of the Beginning in Cotati on May 31 - June 1, 1974, it came up that the Heider's session dated 5/31/74 may be the first known face-to-face meeting between Garcia and the great Ron Tutt, who would hold the beat for Garcia basically from sometime late 1974 / early 1975 until August 1977. In comments, Corry confirmed Tutt's availability based on known Elvis chronologies, and asked when was the "next first-known" Garcia-Tutt meeting. I cited the 12/15/74 show at EMU Ballroom, University of Oregon, Eugene, an attendee of which confirms that Tutt was drumming.
A few quickies. First, there's a review of the 12/15/74 in the campus newspaper, the Daily Emerald, and it sheds no light on Tutt while referring to the band as "Jerry Garcia and Merl Saunders and Friends". Doggy no barky.
Second, the blurb above, from the Oakland Tribune on 1/12/75, represents the earliest reference of which I know to the change of the Garcia/Saunders band (JGMS) into Legion of Mary (LOM), referencing upcoming shows on March 1-2, 1975. The same person who attended the Oregon show remembers these shows as the first to use the LOM name, though I can't remember if I contaminated the informant by putting the data above in front of him/her.
Anyway, I'd love to find an earlier reference to Legion of Mary (outside its catholic church context, of course), but I'd be surprised if there was one. The little blurb above has all the hallmarks of a fresh announcement of a new band, name and all.