2005 is when lenovo started putting their logo on it, I knew there was a ton of thinkcenters branded as IBM but were actually lenovo. they were just re-using the same IBM chassis that IBM designed3 years earlier for the netvista product line, only changes were a bigger PSU hole and a thinkcentre logo on the front.

I remember seeing ThinkPad T42s that were made after a certain point in 2005; they had Lenovo written on the stickers on the underside but nothing more. I've also seen some late production T43s that had the Lenovo logo near the status LEDs. Sometime in 2007 is when I quit seeing the IBM logo on ThinkPads.

thinkpads were IBM branded much longer than the desktops were after the transition... most people still call them IBM thinkpads.