Just a smidge of further clarification on the topic......
Indeed, all 124 sedan glass will physically fit the hole in the body and will connect to the defrost electrical circuit.
However, in reality, there were several different types of 124 rear window glass available, even for different varieties of the cars available in the same model year. These differences were/are based on the tint levels, the type of glass used (single sheet vs. compound glass), as well as the configuration/size of the defroster wires embedded in the glass. There was even glass available that was untinted.
For example, the normal 300E/E320 cars (124.032) used a different rear glass pane (part number 124 670 33 80) while the E500E used part number 124 670 10 80. The US-spec 400E/E420 in fact used the same glass as the normal US 300E/E320 cars, whereas the E500E used the uprated compound/tinted/heat-absorbing glass with the smaller defrost wires embedded.
Of course there were more glass options available for non-US cars than for cars delivered here.
Cheers,
Gerry