Advertising cover with imperf Washington - Oliver Typewriter

Here's a bit of a followup on this one. I noticed the Oliver Typewriter in the illustration is a No.9. So with help from my goggly friends I found this website Type-Writer.org. On this page they write about an Oliver No. 9 that appeared in an episode of the Waltons.
They write, 'I never watched The Waltons as a kid. Nor have I caught up as an adult. This episode, “The Typewriter,” is the only one I’ve ever seen. In it, John Boy borrows an Oliver No. 9 from a pair of bootleggers, er, little old ladies, so that he can copy a story he had written in longhand — a publisher earlier rejected this handwritten manuscript. The ladies claim the typewriter was purchased in 1908, but the No. 9 was manufactured from 1916 to 1922. No doubt a prop, though the ladies might have been mistaken about when it was purchased.'

So I can narrow this cover to that period, during which two imperf 1¢ green Washington's were issued. SC#481 in 1916 and SC#531 in 1919. Sooooo, more research. Perhaps I need to zero in on the slogan cancel.

Stay tuned.

Here's the website. But I'm afraid you can't watch the episode they promise. Copyright infringement caught up with them.

type-writer.org/?p=2162

Thanks for that Steve. I didn't derive that info from my Scott's Specialized.

If I remember correctly, the surface of the engraved stamp will have more texture, due to raised ink, than the offset. Correct?

Wow, I was just about to answer this myself, and you beat me to the punch.
I thought, hey, why don't I look in one of those many philatelic books I've been collecting, that are sitting right here beside me on the bookshelf. So I did, and I checked the stamp and it is definitely offset litho.
That said, I'll stop talking to myself, and stop touching my stamps (I didn't use my tongs)

So, the stamp is a #531, and I have a better idea when this cover was sent.

Thanks again Steve.

Nice find, jamesw . Here is everything you could possibly want to know about the Oliver Building, a Chicago landmark, and Oliver typewriters.

HI all
Back to this Oliver cover again, can anyone i.d. the machine cancel not the second (1923) cover? Unlike an International, the curvy lines start on the upswing, and there are only 6 of them.
Thanks in advance.