The Kingpins
Though often stated to be so Jimi Hendrix actually never was a member of King Curtis & the Kingpins. For the simple reason that King Curtis only started to use the band name "Kingpins" in 1967 whereas Jimi played guitar with Curtis circa 1965 / 1966.
Even though this is basically a largely trivial mistake it`s in my opinion important to properly root it out so I gathered all of the evidence that I have on this page. I went through all of the 1966 King Curtis gig ads that I could find - NO Kingpins. Likewise King Curtis did NOT release any records credited to the Kingpins in 1966.
Yes, King Curtis & the Kingpins did release "Instant Groove" with Jimi on guitar but the track was based on "Help Me (Get The Feeling)" by Ray Sharpe With the King Curtis Orchestra recorded in 1966. The original backing track had Jimi on guitar, as does "Instant Groove", but the basic track from 1966 was reworked and the song credited to the Kingpins in 1969, long after Jimi had departed. The first mentions of the Kingpins, live or on record, only pop up in 1967, Jimi left for England in September 1966.
Below is a list of the line-ups / band names that King Curtis DID use in 1966. There are many different names with a lot of variation in the spelling. In general it seems that when King Curtis was backing up soul / r&b vocalists the band was called "the King Curtis Band" or something close to it. On other occasions the band name seems to have been dependent on the actual line-up and / or the type of music being played.
LIVE DATES
Here are "sample" ads of all of the different line-up names used in 1966 that I was able to find, not a single one had the band booked as "the Kingpins". (PLEASE NOTE: I`m not suggesting that Jimi did or didn`t play any of these dates, I´m just discussing the band names here...)
Tue, Feb 8, 1966 – 18 · The Boston Globe (Boston, Massachusetts) · Newspapers.com
The King Curtis Band
Saturday 12 February 1966
Brandeis University, Boston Massachusetts
Fri, Mar 4, 1966 – Page 40 · Philadelphia Daily News (Philadelphia, Pennsylvania) · Newspapers.com
KING CURTIS
28 February - 5 March 1966
Saxony West, Philadelphia, Pennsylvania
KING CURTIS COMBO
Not a live date but related: the "R & B Agencies" artist listing in the Record World 12 March 1966 -issue lists the "King Curtis Combo" as a client of Shaw Artist Corporation. 
Sat, Mar 19, 1966 – 11 · Hartford Courant (Hartford, Connecticut) · Newspapers.com
KING CURTIS SEXTET
18-20 March 1966
Romano`s Steak House, Hartford, Connecticut
Sun, Sep 18, 1966 – 114 · The Boston Globe (Boston, Massachusetts) · Newspapers.com
KING CURTIS Quintet
Sunday 18 September 1966
Paul`s Mall, Boston, Massachusetts
Sat, Oct 1, 1966 – 11 · Hartford Courant (Hartford, Connecticut) · Newspapers.com
King Curtis & his Orchestra
Saturday 1 October 1966
Bushnell Memorial, Hartford, Connecticut
RECORD RELEASES
In 1966 King Curtis released the following lps & singles as a solo artist:
Albums
Credited to King Curtis:
That Lovin` Feeling (Atlantic 33-189 (mono) / Atlantic SD 33-189 (stereo)) May 1966 USA 3
Credited to King Curtis:
Live At Small`s Paradise (Atco 33-198 (mono) / SD 33-198 (stereo)) October 1966 USA 4
Singles
Credited to King Curtis:
"On Broadway / Quicksand" (Atco 45-6406) March 1966 USA 1
Credited to King Curtis:
"You`ve Lost That Loving Feeling / Make The World Go Away" (Atco 45-6419) May 1966 USA 2
Credited to King Curtis:
"Dancing In The Streets / He`ll Have To Go" (Atco 45-6429) August? 1966 USA 5
Credited to King Curtis:
"Pots & Pans - Part 1 / Pots & Pans - Part 2" (Atco 45-6447) October? 1966 USA
Credited to King Curtis:
"Something On Your Mind / Soul Theme" (Atco 45-6457) December? 1966 USA 6
SOURCES
1 the single is often listed with "Quicksand" as the A-side but white label copies come with "On Broadway" labelled as the "plug side" so the correct pairing is "On Broadway / Quicksand" (Atco 45-6406) March 1966 USA. "On Broadway" was recorded on the 4th of March 1966 and the 45 was reviewed in the 26 March 1966 Cash Box issue (with "On Broadway" listed as the A-side) so the single was released in mid/late March 1966.
2 The 28 May 1966 issue of Record World reported that "a new King Curtis will be released shortly", 45cat.com has images of a white label copy with "KCLU 5/23 -66" written on it (indicating it was received / added to the library of California radio station KCLU on 23 May 1966 - if genuine of course) and the 45 is listed in the 28 May 1966 issue of Billboard under "Chart Spotlights" (Billboard was published roughly one week in advance of the cover date).
3 the That Lovin` Feeling album is included in a listing of covers versions of the song "The Shadow Of Your Smile" in the Cash Box 7 May 1966 issue though it seems it wasn`t actually released yet. A review of the album appears in the 11 June 1966 Cash Box issue, a month later. So a probable release date is mid / late May 1966.
4 Live At Small`s Paradise is listed in a Cash Box 22 October 1966 news item about October 1966 album releases on Atco
5 the 45 is listed in the 20 August 1966 issue of Billboard under "Chart Spotlights" (Billboard was published roughly one week in advance of the cover date).
6 reviewed in the Cash Box 24 December 1966 issue
KING CURTIS