Srila Prabhupada does in fact give the adequate title of chapter six of His Bhagavad-gita As It Is.
It is definitely not Sankhya-yoga, as per Macmillan edition.
It is not Dhyana-yoga, to a lesser degree, as per current official edition. Dhyana is only one of the “angas” or limbs of the eightfold yoga system, as we all know.
Clearly and strongly, Srila Prabhupada gives the key to this 50 (fifty) year old question in the very first sentence of the purport of the first verse of chapter six as follows:
“In this chapter, the Lord explains the process of the eightfold yoga system as the means to control the mind and senses.” The first part of the sentence itself: “In this chapter the Lord explains the process of the eightfold yoga system……” is self-sufficient and self-explanatory. As always Srila Prabhupada is clear, concise, strong, and straightforward.
This is indeed the wording of the original transcript (OT), which is perfect in itself, and in both Macmillan and official versions this original wording has unnecessarily been changed to:
“In this chapter the Lord explains that the process of the eightfold yoga system is a means to control the mind and the senses.”
There is a shift of emphasis which covers and ruins Srila Prabhupada intended meaning.
Yes, this is a fifty-year-old question. And I remember how in the early days and later also I was trying to adjust my mind any possible way to understand how the sixth chapter of Bhagavad-gita is related to sankhya-yoga. It was a bit of a mental agony. As far as possible, we should carefully avoid causing people mental torture.
As always the Original Transcript of Bhagavad-gita As It Is is a superior spiritual text in its own right with the power to correct many mistakes and answer many questions. I had already expressed this consideration in my 2022 Vyasa-puja offering to Srila Prabhupada. Unfortunately, my offering did not pass the censure and consequently was not published where it should have been. But my point stands: Bhagavad-gita As It Is Original Transcript available here https://bookchanges.com/bhagavad-gita-as-it-is-manuscript/ is a spiritual text on its own rights and with its own unique spiritual inspiration.