I am not sure the term "retconned" applies here.
I don't see why not. TWOK's makers weren't nearly as concerned about continuity details as we fans tend to be today. That's true for most people making sequels or revivals; they use what they like and change what gets in their way. (Like how every
Planet of the Apes sequel in the original series retconned something about the previous movie while pretending to be a continuous sequence. Or, to draw on Harve Bennett's own career, the way the series version of
The Six Million Dollar Man ignored or rewrote many details from the pilot movie for same.) They tweaked a number of details for TWOK, like the age and ethnic composition of Khan's followers, the presence of Chekov for the original events, the available costuming and technology (Khan's people have a movie-era medical monitor in their compound and Khan wears a broken TWOK-era uniform belt buckle as a medallion, neither of which existed when they were stranded), etc. Not to mention ignoring all the previous times that Kirk had faced the death of someone dear to him (Gary, Edith, Sam & Aurelan, Miramanee and his unborn child). Not to mention giving him a never-before-seen old flame and illegitimate son, one of the corniest, most cliched kinds of retcon from '80s/'90s TV. (See also Steve Austin's never-mentioned son in the first bionic revival movie, and MacGyver's hitherto-unknown son in his series finale, which was meant as a potential spinoff pilot.)