As per my understanding, COPR expiry and your ready to travel webform plays a vital role for 4 pointer email. I have also seen people who have not raised the ready to travel webform but they also received the 4 pointers email.
So, anyone on, before or after March 18 with "expired" COPRs, will definitely be receiving this 4 pointer emails.
Sending out the bulk email notification is set up by CIC from last week itself, so I will highly recommend you guys to wait for sometime and you'll see the email within next two weeks for sure (in next ready batch). These are my inputs on your query, hope this helps.