the locking lever on my wifes chapuis iphisi is pretty close to centered (looks perfectly centered to the naked eye.. Ive never actually measured it)..
that said none of my double shotguns.. to include both SxS and OU are perfectly centered.. all of the are off at various angles.. these include beretta, webley and scott, and AyA guns.. being off center has never created any sort of functional problem, so Ive never really given any thought to it or worried about it..