FASA had the license for a ST role playing game in the 80s, and they employed ST author John M Ford ("The Final Reflection") to give his slant on Klingon society for their Klingon manuals. In his novel, he postulated that TOS Klingons were actually human/Klingon fusions, which were used as a servile race by the bumpy-headed Klingons. There were also Vulcan/Klingon fusions and Romulan/Klingon fusions.
Minor correction: The Human-fusions weren't servants of the Imperial Klingons. True, Gelly/Kelly is mocked as a child, but in the end a Klingon is a Klingon regardless of appearance. Also, there are Rom-fusions, but not Vulcan-fusions as the Klingons did not want to mix their blood with that of pacifist vegetarians (per the aforementioned RPG manual). Perhaps you are thinking of tharavul?
Although, drawing from a term used in TNG, the Chris Claremont graphic novel, "Debt of Honor" (which also used some John M Ford material), claims that the whole human/Klingon fusion subspecies was discommendated around the time of TMP.
True as they had gained majority power during the time of the series but suffered humiliating setbacks at Organia, Sherman's Planet, and, in DoH with the gunship. The discommodation was politics not racial prejudice. It's likely the H-F's made up only a few lines having been around only fifty years or so. With a relatively small population they could easily be exiled to a hostile area outside Imperial space, no doubt after a little civil war. Such an action along with the cessation of any future creation of the fusion program and they would be all but gone from the Empire by the TNG era. It also might be something Worf wouldn't want to talk about.
Despite how Michael Dorn mispronounced it in "Sins of the Father," the word is discommENdation, not discommodation. To discommend something is to disapprove, blame, censure, put into disfavor or ill repute (naturally, the opposite of "commend"). To discommode is simply to cause inconvenience or trouble.
Since that bit was speaking of FASA, actually there were only two featured in addition to the Imperial Race (i.e., baseline Klingon): Human- and Romulan-fusions. (This was supposed to be part of a "know thy enemy" philosophy, taken to exreme ends.) It was, however, stated that there were other, less numerous fusion types. In The Final Reflection, Ford neve mentioned the Romulan type, but did hint that there were many types. Spoiler: Kelly's fusion type Gelly/Kelly was speculated to be an Orion-fusion, but testing showed this not to be the case. Krenn has to go outside normal channels (WAY outside, as in McCoy's grandad) so she can find out what sort of mix she is (not that we're told). So there are obviously enough types so that there's room for that kind of uncertainty. .
Did Chang ever say anything like: "Tukuy kay pachaman paqarimujkuna libres nasekuntu tukuypunitaj kikin obligacionesniycjllataj, jinakamalla honorniyojtaj atiyniyojtaj, chantaqa razonwantaj concienciawantaj dotasqa kasqankurayku, kawsaqe masipura jina, tukuy uj munakuyllapi kawsakunanku tian." ? whoops... that's Quechua...