Interior Cabin Filters on 2005 E-Class

I own a 2005 E500 wagon w/4-zone climate control (Thermotronic - Equipment code 581).  From what I have read and seen on video on the Mercedes Medic site, a W211 w/Thermotronic also requires two interior cabin filters, in addition to the one in the engine compartment, that are located under the passenger side dash.  I got the filters and go to put them in, but there are no access ports for filters in this location on my vehicle.  Am I missing something, or are the interior filters not required on ALL W211 vehicles w/Thermotronic?