Question you would probably know the answer to: The Wikipedia article on Line 2, in the section titled "Depot", suggests the line isn't using the newest trains because they can't be stored at the Greenwood yard.
"The Greenwood Yard will be inadequate as it is completely full with no room to expand, and because its facilities are optimized for two-car train sets rather than the six-car train sets of the proposed new fleet."
From that, I gather that when T1 trains are put in the yard, they are broken down to 2-car groups, and that's why they can't hold the Rocket trains, or at least, not enough of them. Is all that still true?