I don't know exactly when the change took place, but it must have been between September and December 2022.
I see some names that were changed way earlier than September 2022Yeah, if that's for security reasons, we need to respect them and IMO, if my username changed, I don't want to disclose who I am in the past. 
Because it's useless changing your name if everyone knows who you are, not unless you want to change your username for the brand name of your company.
It's actually hard to hide who you were from the past, especially with the quoted replies. Your new username will still be associated with posts and quoted replies having your old username.Because it's useless changing your name if everyone knows who you are, not unless you want to change your username for the brand name of your company.
Also, there are now third party sites that keep track of forum data like Loyce.club, bpip and ninjastic.space. Someone can still easily connect the dots using those sites.