The only post 1930' spanking mention I know of in
Etta Kett.

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There are at least five OTK M/F spankings to be found in the comic strip Etta Kett in the 1930s

. So why would all the spanking action come to a sudden stop after Paul Robinson had previously been using spanking gags year after year

I'm guessing that for
one, the joke of Etta getting her comeuppance with a spanking wore thin for Robinson as the decade of the '30s started to wear down. He unfortunately seemed to have a problem coming up with an original gag that would involve spanking Etta and anyway one M/F spanking per year in a strip not named Oaky Doaks is really quite unusual. So the idea of him letting it go for a few years does seem a possibility. But
two I think that if Robinson intended to renew Etta's spanking down the line in his strip that notion was spoiled by World War II.
So Etta joins the war effort with mixed results. She does complain, early after the U.S. enters the war, about how ten of her boyfriends have been drafted but she does her patriotic part and pitches in at one of her dad's factories [The Kett family's wealth varies wildly over the years]. She also did her part in the war by entertaining the troops...lots and lots of troops

I would imagine that after maturing his leading lady this way Robinson found it more difficult to have her spanked like a high-schooler even though in the later years of the strip Etta did indeed find herself back in high-school.

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And
three the strip makes a dramatic change moving from the forties into the 1950's. Etta is no longer to be found in a range of jobs from airline stewardess to movie stand-in or in a long series of broken engagements to be married. Instead she settles down...down and down even further all the way back to high school. In a future post I'll show you how she starts out as a young woman who must be in her mid-twenties but ends up 48 years later as a typical and stereotypical comic teen. One would think that Etta the high school senior would be a good candidate for spanking but as in most of the other pretty-girl teen strips of the second-half of the 20th century that fate is only ever vaguely implied.
Below is the last Etta Kett I could find and it offers the usual family oriented innocent gag. As of November 2, 1974 the strip abruptly ends in every newspaper I have available through my archive [Paul Robinson had died on September 21, 1974. at the age of 78]. The strip is listed, according to some resources, as ending on November 24th but I can't prove it.

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