As per the photo suggests, I think we may be the only mass rapid system in the world to use a first generation train (Mark I) all the way to the 5th generation train sets concurrently along the same routes. Taking the train at Expo line is like experiencing a historical transit journey of the past 45 years.
When Mark I sets were first making their inaugural runs, the then Prince Charles was still with Princess D, and both Q.E. and Queen Mother were still alive and relatively young.
Even Toronto has recently gotten rid of their Bombardier Mark 1-only Line 3 at Scarborough.