Question re heater defroster ducts

[rons49]

I saw some prewar cars for sale on Ebay and noticed that they had registers in(on) the dash for a defroster. Since heaters were optionable, and I presume the defroster with it, did the manufacturers build all dashs as to accept heater defrosters whether ordered or not? Or, did the restorerowner just never put the system with hoses etc. back, leaving an opening through the dash top?

[Jon37]

As far as I know the manufacturer would have put slots (for the defroster outlet below the windows) into all cars (heater-equipped or not). If the slot was prominent it would have been filled with some sort of delete plate or cover, which could then have been removed if an actual defroster nozzle was eventually installed beneath the dash. (Some vent slots would have been so subtle that there'd have been no need to plug them).

In my case (a 1937 Terraplane) since there was no original factory heater a sort of grille (a place-holder) was fitted over the defroster opening to finish it off. I removed the grille and bolted an original-type defroster nozzle (which I'd acquired, along with a heater) in place under the dash. The nozzle had its own deflector, which poked through the slot in the dashboard and finished off the hole. I'm willing to bet this was standard practice amongst all the companies.