Ofcourse it doesn't make sense to skip the earlier AoRs and start working on later ones.
IMO, there could be two reasons, namely, and I believe both are intertwined:
1- IRCC has delayed whole test thing to the breaking point. Now, they are in damage control mode, and trying to speed up processing wherever they can. To control a damage, easiest way is to process applications that are still within 12 month time frame (from AoR) which makes Nov, Dec 2019 and January 2020 AoRs a priority over predecessors. What IRCC will achieve out of this : by cherry picking approach, they will be able to meet KPI of processing applications within 12 months time frame.
2- One may think what is the reason for picking 12 month old application than 16 or 18 months old applications? To control damage, one would look easy fixes first so to make most in the race against clock. We know that criminal and security checks are valid for 12 months (which I believe starts some weeks after "in process" stage). I believe those security checks expire after 12 months. Therefore, IRCC would have picked files with valid security checks. What message outside world is getting: the processing has resumed albeit a large majority is still waiting for test invites.
My worry is the backlog of applications where security/criminal clearance has expired and IRCC need to initiate those checks again. Having said that, I sense that the sequence of applications will be as follows:
Pandemic files (where IRCC offices were closed until Nov notification):
1-Those with valid checks will be processed to move to the next step. This is happening now.
2- The files with expired checks need re-work. I have not seen 16-18 months aged applicants receiving an invite for test yet. Whenever it start, it will be the begining. However, this has not started at this point in time.
Post Nov notification:
3- These applicants may probably be processed to continue to meet KPI (12 months). Keep in mind there are paper based and online application systems in place now.
4- Online applications will actually be processed faster than the paper based family applications. Online application system is brand new but once it is up and running, families would also be able to submit online applications.