Were these silver cad or something else? Talking about the one that also holds the blower motor shield in place along with the heater box as well as the two small bolts that hold the shield in place.
Have only found silver cad/zinc plated ones on 69 San Jose built cars as far as the stamped nuts go for both the heater to firewall and the one shield nut on the ps upper stud
Same for the two hex headed screws
Amount and location of sealer depends on the pattern the worker applied and the angle of application
A few examples for illustration
Really well maintained original
Spray sealant didn't leave any shadow in this area of the firewall around the heater motor in this example
In this one you can see that some of the remaining sealant did leave a shadow under the bracket