Can the Backs of Teeth Be Bonded to Add Thickness and Contour?

There is an art to making front teeth, both the outside that shows to the rest of the world, and on the insides that you feel all the time with your tongue.

My hunch is that your old porcelain veneers were actually too thick. That would have been very common if your old veneers were 25 years old.

It may not really be a question of right or wrong. At this point it may be more a matter of preference. Tell your dentist that you prefer the thickness of your old veneers. Most of the time bonding can be done to thicken them. 

BUT... if the backs needed to be porcelain (more like crowns than veneers) then it's typically not possible to add porcelain reliably here.

Try it for a little longer. The front of your bite actually ought to have some overbite feel to it.

Like other concerns, speak with your dentist and see what the options are.

Can you have it done, YES, would I have it done not really.  I would have the dentist remake the veneers if in fact they were overadjusted.