But IMHO it would have been wise to push people to register for this early
Which is what the electoral commission did. They were even briefing during radio news (multiple channels) on Monday morning stating that leaving registration until the last minute would be unwise since that may mean that people would be unable to register in time for the deadline. It's difficult to see how they could have been any clearer about the risks, and let's not forget everyone of voting age is obliged by law to register not five seconds before a deadline, but in Autumn of the preceding year and to notify the electoral registration officer if their details change.
Here's the advice given about registration:
"With 'rolling registration' in force, it means that the register is updated every month. However, applications need to be received several weeks before publication to guarantee inclusion "
"An annual canvass still takes place every autumn to ensure the register is up-to-date. There is no monthly update during September, October or November during the annual canvass period when all households have to register. A new Register is usually published on 1 December."
Isn't that clear?