If the house was totally rebuilt in 1980's, even if the foundation is original, the build date is 1980's not 1940's (tho many agents will put some reference about that in the listing, tho it's not necessary). The house should be priced according to what is it, where it is, how many bedrooms/baths etc,.
If you bought a resale that was built in 1940, then gutted the place and replaced electrical, plumbing, kitchens, baths, floors etc,.... when you went to sell it would you expect to get less because it's original build date was 1940???
A house that was built in 1940 does not necessarily mean that the house is worth less than a house built in the 1990's or early 2000. You have to take the effective date of the house. There are houses built in the 1990's but the inside could look and feel like they were built in the 50's.
The improvements and upgrades done to the house should be taken into consideration and these factors may add up to the value as adjustments in determining the current market value of the house.
If they completely rebuilt the house in 1980, then that is the construction date and the original 1940 would be irrelevant (if the house was completely burned down by the fire - it doesn't exist any longer).