Hey, I realise you probably didn't mean to do this, but using a previous name of someone who's transitioned is not a good thing to do.

Why? An overwhelming majority of this academic's papers [1] are published as Paul Hasler.

[1] http://hasler.ece.gatech.edu/Published_papers/index.html

I know a professional accountant who kept using her maiden name in business contexts after marriage because otherwise people had a hard time finding her skillset and work history etc., but for all other purposes she’s Mrs $NEW_NAME.

As regards trans names, I’m told quite a lot of people (not 100%) find their old names an uncomfortable reminder of an uncomfortable past.

Plus it’s a sign of respect to use someone’s chosen name, and a sign of disrespect to use any other name — for non-trans examples, what does it say about someone’s respect for the other party if they call David Tennant “David McDonald” or Boris Johnson “Alexander Boris de Pfeffel Johnson”? (At least, without the brackets that the previous poster used; with is useful for the same reason as my friend using her maiden name, but it’s still often frowned on).