"Spock's Brain" is probably the most MST3K worthy episode in TOS. So nit-picking it is gratuitous.
..at least we were treated to TOS' only ice covered planet! Very cool/interesting stuff!
Then there's the reference to Stratos as "cloud city" in "The Cloud Minders."
Hmmm....cloud cites (with orange-hued skies to boot!) and ice planets in the same season....sounds VERY familiar...
George Lucas must have watched a lot of season 3 and recalled that when writing The Empire Strikes Back