That ESB image has always confused me in regards to the shoulder bells, as they look so different than usual.
From everything I've encountered during my research into Vader's costume, there is no difference between the ESB and ROTJ shoulder bells. The difference in appearance comes from them bells being flush with the shoulder armor (like in that ROTJ shot), or the bells hanging slightly underneath the armor as it was mostly throughout ESB.
Seeing that shot of the HT ROTJ, it looks like HT simply sculpted the bells wrong. They are attached flush to the armor like in ROTJ, but the bottom edge is sculpted as if it's hanging underneath (angled differently, making it appear longer and more rounded).