Shvegel,
Originally there was not "carpet" under the driver's or passenger's feet, only floor mats. Either you have carpeted floor mats or you have historically carpet. It's probably not uncommon to have the carpet replaced incorrectly during a restoration by someone who didn't know any better on this unusual point.
Thanks,
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420