I've found no other way to view my own old posts, searching my previous names only returns posts of mine that others have quoted.

Firstly searching your old name wouldn't do anything - when altering your display name it changes it EVERYWHERE - even your old posts will display your most current name.

 

Secondly there is no way that I am aware of, but the year cut off is pretty generous I mean if its a thread you care about you ought to be posting there at least once a year or have it favourited or followed really. More than a year would get to heavy for the system to handle the requests for some users without lagging the forums or taking ages to load - I mean I have 16 pages in my content and that's quite empty by my standards.

Searching your old name brings up every post of yours that's been quoted, since quotes don't update when you change your name.

And I understand that pulling every post would be hard on the server, but if you could select a 1 year timeframe it wouldn't be any harder on the server than what it does now.