I'm looking for some AC flights between BOS and YYZ in mid-November 2019.

Until the end of northern summer 2019, these flights are all operated by AC mainline using three-digit flight numbers in the AC5xx series.

From the beginning of northern winter 2019/20 (ie 27 October 2019), AC, ITA and Google Flights show a mixture of AC5xx flights and Air Canada Regional AC7xxx flights.

However, EF's flight availability display is only showing AC7xxx flights from this time, and the EF display doesn't match what is shown by the other channels.

Taking 15 November 2019 as an example, all sources show seven of the AC7xxx flights. However, EF additionally shows AC7621, which the others do not show; and the others show AC523, AC525 and AC531 which do not appear on EF.

More curiously, EF will return seat maps for AC523, AC525 and AC531 if the details are input manually, even though the flights do not show up on the availability display.

Is there any obvious explanation for this odd mismatch between sources, and between different EF displays?