First of all, there is a report coming soon about changes to the roll out of routes and it could be this month.
514 wasn't part of the first roll out, but since it service the main centre of 504, it leap frog other routes in 2016 and to have 10 cars this year first.
511 has been push down the list because streetcars can't run on it until the Bathurst Bridge is rebuilt which is a City project.
505 is the next route. Even if BBD delivery the plan 40 cars this year, TTC is going to be short cars for full conversion of routes plan for 2016 that has been moved to 2017.
As for 4431 entering service on Sat, this is a new one how it took place. In the past, once cars have done the final test on 506, it sat in the service bay from 1 to 5 days before entering service. 4431 was out for testing on St Clair early Sat morning and was sitting in the service bay at 10:30 am and then went into service shortly after that time frame. A very quick turn around compare to the rest of the fleet to date.
As noted, cars were on 504 due to the closure of QQ and Union Loop since drivers are already sign up for this board change. TTC had to put the drivers of the new fleet somewhere and decided to use 504 for them. Riders were given a taste of what to come for them in the next year or 2 this weekend.