...Alan Dean Foster had been asked to supply a two-part Klingon script for a fourth season.
You're somewhat misremembering what you said in 2008, Therin old pal.

In the latest trade omnibus reprints of the TAS adaptations ("Star Trek Logs"), Alan Dean Foster explains that the final two-thirds of "Star Trek Log Seven", about Kumara the Klingon, was actually from a two-part script he pitched, and then wrote up, during Season Three of TOS. When he submitted it, he was asked to resubmit... "if" there was a Season Four.
Sounds like he wrote up the script on spec.