The Washington Post article below reproduces three "Hagemeyer" strips
that don't seem to have been widely published before.

https://www.washingtonpost.com/arts-entertainment/2021/05/31/charles-schulz-hagemeyer/

Maybe some r.a.c.s. readers were already aware of these strips, because
they came to light in 2020 when they were sold to the Schulz Museum,
but the Post article was news to me. I do of course own Chip Kidd's
book "Only What's Necessary," which reprints (about halfway through
the book) the four Hagemeyer strips whose existence was publicly known
at the time. The three "lost" strips, among other things, solve a minor
mystery about the four strips reprinted in Kidd's book, which were
numbered "1," "2," "3," and "5." The "lost" strips are numbered "4,"
"6," and "7."

One can plausibly infer that Schulz made a serious attempt to pitch
"Hagemeyer" to United Feature Syndicate, but it seems that at this time,
there are no known records of such a conversation. But fortunately, the
strips do exist, and the Schulz Museum plans to exhibit them starting on
June 17.

---
Tim Chow