The show that replaced the Andy Griffith show, Mayberry R.F.D. was name to indicate how rural it was. RFD being a common term for Rural Free Delivery at the time, i.e. the sticks.
Anecdotally, in the UK, I shipped a Raspberry Pi from Bath to a guy in Scotland. I looked it up on Google Maps, and it was in the west and to the left of nowhere.
24-hour overnight, guaranteed 1 PM delivery. Not very expensive; shipped at 2 PM, and he told me he had it in hand the next day at 10 AM. Trains, Planes and automobiles, if I could have found the place, I could not have beaten that.
I used to live out in the sticks amongst New Zealand farm land. Though we lived in a village so had a regular street address, anyone between towns, i.e. Farmers, usually had RD1 / 2 / 3 addresses, meaning “Rural Delivery.” Presumably the Post Office had lists of farms by surname or some other divisioning for the really remote places, and local knowledge was the way you deliver mail. I think it was twice-weekly, too.
When I was a kid I remember our mailing address still used a rural route number. Realizing that I had a resource for actually dating the change, I just looked at my scanned copies of the family’s old church directories, which had mailing addresses in the back.
In 1967 it was just the route number and town. By 1974 an area code was added but the route was still there. Between 1984 and 1987 a road address was added and the route number removed. (I don’t know if the road actually had a name before then, I do remember that at some time in my childhood road name signs were first added.)
The progression was:
1967
Darren’s Family
Route 1, Smalltown
1974
Darren’s Family
Route 1
Smalltown, 12345
1984
Darren’s Family
Route 1
Smalltown, 12345
1987
Darren’s Family’s
123 Local Road
Smalltown 12345
(None of them included the state name between town and zip code.)
I interpret that in the context of his statement that the change happened “between” those reference points. He has them as bookends, and is offering them as such, but has no further granularity in the data. The previous data point was in 1974, which means, without the 1984 data point, the 1987 address had 13 years in which it might have been introduced. But this way, we see the old format was still effective a decade after the change in 1974, and the actual change window is much narrower.