It was Margaret Hamilton as Cora, a part she took, admittedly,
to soften her image.
I don't think Monte Markham's Perry Mason ever lost a case,
but the show was often criticized for scripts so complicated
that even Markham/Mason was surprised when the real guilty
party stood up and confessed.
But we've gotten 'way off topic. I'll give you another example
of a station that substituted one network show for another:
WCPO Cincinnati, when it was a CBS affiliate in the '70s, routinely
pre-empted "Love Of Life" at 11:30 AM and substituted (usually)
the 10 AM show ("Uncle Al" was on from 9-10:30); in my Kentucky
listings I've pointed out Ch. 9 showing "All In The Family" at 11:30
when it aired on CBS at 10 AM; the station would sometimes air
"Tattletales" at 11:30 rather than 4 PM.
WBTV Charlotte was notorious, all through the '80s, for airing "The Price
Is Right" on a day-behind at 10:30 AM in order to carry its local "Top O'
The Day" from 11:30-12:30. That meant the pre-emption of CBS's 10:30
show, such as "Press Your Luck" and "Card Sharks." Viewers in Charlotte
had to be able to pick up WFMY Greensboro or WSPA Spartanburg, SC
(which, IIRC, was carried on cable anyway) in order to watch the shows
WBTV pre-empted.
Speaking of WFMY, it had a habit up until about 1958 of replacing one
CBS show with another; a couple of examples: "December Bride," which
aired on CBS Mondays at 9:30 (ET), was on WFMY Sundays at 9:30, and
"Alfred Hitchcock Presents," the network's show at that time, was at first
pre-empted, then put into a late Saturday timeslot. WFMY also pre-empted
CBS's Friday 7:30 show in 1956 to air "Do You Trust Your Wife?" (in-pattern:
Tuesday 10:30 PM). The station liked to take advantage of hammocking and
put a popular syndicated show between (or after) popular network shows,
so it would do its own thing Mondays between "I Love Lucy" and "Studio One,"
Wednesdays between Arthur Godfrey and "I've Got A Secret" ("The Millionaire"
aired before primetime on Fridays for about three years), and Sundays between
"GE Theater" and "The $64,000 Challenge." WFMY was not alone among CBS
affiliates that preferred to do their own thing after "The $64,000 Question" on
Tuesdays.
And look at any primetime schedule for WKRG Mobile prior to the mid-'70s; I
guarantee you'll find one CBS show in place of another somewhere during the
week.