All the tour itinerary lists I've seen have Queen playing the Orpheum Theater in Boston on 4/26/74. After digging through some archives, I found out the following information:
- TWO shows were scheduled to be performed on 4/26/74; according to an ad in an underground newspaper, "Due to Popular Demand, a second show has been added at 10 p.m."
- According to a 1975 article in the Boston Globe, the band was getting a third chance to play Boston because their 1974 shows were cancelled. The 4/26/74 shows were cancelled "when a member of then-headlining Mott the Hoople became ill.
- According to a 1974 Boston Globe article, promoter "Don Law has rescheduled the previously sold-out Mott the Hoople Queen program for May 13 at the Orpheum."
- The 1975 Boston Globe article mentioned that the band didn't play the rescheduled 1974 date either. The article states: "The last time I was here I turned a nasty yellow color, guitarist Brian May recalled, succinctly describing the hepatitis which befell him in Boston last year, sending him on a horror-filled night flight and prematurely ending Queen's first American tour."
It's pretty safe to say the first time Queen played Boston was on February 15, 1975 when they played two shows at the Orpheum Theatre. According to a Boston Globe review of the show, Lynyrd Skynyrd was also on the bill for the first show, but cancelled out:
"When a second show was added, Skynyrd apparently declined the offer to play the back-up role twice in one night. The two groups had toured together in Germany late last year and word has it that the American fellows did not get along well with their regal companions. Even though still scheduled to open the early show, Skynyrd was scratched at curtain time 'due to unforseen circumstances'."
Mahogany Rush supported Queen for both performances.