Other mistake: When the boys are playing football in the backyard, watch Greg's right foot - at one point he slips on the Astroturf lawn, causing it to wrinkle and exposing a seam on the "grass" lawn. (00:03:20)
Suggested correction: At no time in the show did they affirm the grass in the backyard is real. Many houses, particularly out west where the show takes place, have artificial grass as it's often easier than caring for real grass which tends to dry up easily out west or not grow at all in some areas. Even in A Very Brady Renovation they made sure to use artificial grass for the backyard.
The grass is supposed to be real. There are several episodes where they are mowing the lawn.
But the renovation show was in 2019. In the early 70s artificial grass was only starting to be adopted in sports stadiums. Not used in homes until many years later.