Widow needs help: Sennheiser HD650 headphones

Hi All,
I’m a widow at the tail end of selling my husband’s estate and I'm trying to sell his Sennheiser HD650 headphones.

They're in great condition--both cosmetically and working-wise. In fact, they look like they were barely even used. The foam padding on the inside of the headband & the ear pads look brand new  I've got the original box and the original hinged box with the foam inside that the headphones rest on.Those are in wonderful condition. I've also got the cable adaptor--the only thing I don't have is the user manual. 

I had a potential buyer inquire as to when these were purchased as he said this model has changed over time. I know they were purchased in Sept. 2011. 

When I go to HiFiShark dot com & click on the links for the headphones that have sold in the U.S. & in the same condition, I'm not seeing where people have specified what year the headphones are from. Or am I blind? Does the year make a difference?

Thanks~