Who Actually Manufactured Frederick Post Brand Slide Rules?

Before WWI
Dennert and Pape was the manufacturer of "Frederick Post" brand slide rules in the 1903 and 1910 catalogs.  (The Frederick Post Company was organized in 1896 but at first they were little more than a blueprint shop.  1903 is the first catalog I have.)  It's not unreasonable to assume that D&P continued manufacturing Post slide rules until trade with Germany became difficult about 1916.
WWI - 1924
I suspect that during WWI there were no "Frederick Post" brand slide rules.  Post was selling whatever American-made rules they could find--likely including Richardson Direct Reading rules but probably nothing with the explicit Frederick Post brand name.  It appears from the 1921 Frederick Post Catalog that Post was selling some leftover pre-war Faber rules--describing them in the catalog as "Post" brand--but I doubt that they were actually marked "Frederick Post" (certainly, no such specimens have survived).  The first actual "Frederick Post" brand rule after WWI was likely model 1444, a ten-inch Mannheim made by Koch, Huxhold & Hannemann of Hamburg.  Model 1443, a cheap student rule, was made by Albert Nestler about 1923-24.  There were two other "Post" brand rules during this period but I know of no specimens of either.
In 1925 Post began selling a full line of eleven Frederick Post brand slide rules and thirteen unconventional Post "Ritow" rules.  All these slide rules were made by Koch, Huxhold & Hannemann.  KHH was strictly a custom manufacturer of other sellers slide rules; there is no KHH catalog to cross reference Post rules to.

Koch, Huxhold & Hannemann was founded in 1909 by three former employees of Dennert & Pape, and not surprisingly, KHH slide rules are very similar to D&P rules.  The slide rules KHH made for Post in 1925-30 use the D&P DRGM 192052 friction adjusting mechanism.  (That DRGM expired about 1909.)  The picture of the D&P friction adjusting mechanism in the 1925-30 Frederick Post Catalogs led me to misidentify the manufacturer in the Journal of the Oughtred Society, Spring 2011.   I am indebted to Georg Schreiber whose book "Koch, Huxhold & Hannemann, Der Unbekannte Rechenstabhersteller aus Hamburg" is the definitive source for information about KHH.

Hemmi replaced KHH as the manufacturer of all  Frederick Post brand slide rules in 1931.  Except during and immediately following WWII, Hemmi remained Post's supplier of slide rules until they both went out of the slide rule business about 1975. ( As of July 2011 the Hemmi Company was still in the custom plastic manufacturing business in Tokyo.  In 2005 Hemmi made about 400 eight-inch slide rules to a new design of the Hemmi Slide Rule Collectors Club of Japan.  Those slide rules are marked model "P135K.")
During and immediately after WWII Frederick Post brand slide rules were made by Grafton Plastics Company and The Roos Company.  Grafton Plastics was operated by Millie Ludwig and her husband in Grafton WI.  They made two all-plastic slide rules.  Grafton Plastics marked the rules with Post, Dietzgen, Bruning, Compass (and probably other) brand names and model numbers and shipped the rules directly to Post/Dietzgen/Bruning/Compass distributors.  (A subsequent company with the same "Grafton Plastics" name is unrelated to the slide rule manufacturer.)  (Information from Millie Ludwig.)

The Roos Company, New York City, was organized in 1941 to manufacture and distribute slide rules and other products to fill shortages due to WWII.  Their products were branded "Roos," "Charvoz" and "Charvoz-Roos."  (Andre Charvoz was president of the Company.)  The Roos Company was dissolved and reincorporated under the Name "Charvoz-Roos" in 1946--about the same time they  ceased manufacturing slide rules and began importing Hemmi and Aristo rules.  (A fair number of Aristo-made "Charvoz" rules appear each year on eBay.)  Charvoz-Roos entered receivership c1954 but Andre Charvoz continued in the import business as a private person.  He died in 1969.  I can't find any evidence that anyone named "Roos" was ever associated with the business.  (Most information here is from the International Slide Rule Museum.)

What Happened to The Frederick Post Company?
The Frederick Post Company was sold to Teledyne about 1970; slide rules began carrying the "Teledyne-Post" label about 1972.  Teledyne Post gave up selling slide rules about 1975.  Teledyne sold Post to the Phomat Corporation which changed its name to "Post and Company."  Post & Company was acquired by Azon Corporation (which also acquired K&E about 1982).  Part of the Post & Company business was absorbed into Azon, while the remaining portion became "Media Design Corporation," a wholly owned subsidiary of Azon.  Azon was, I believe, primarily in the reprographics business.  Azon has gone through a couple of "reorganizations" but I believe still owns the Frederick Post and Keuffel and Esser brand names.  (Some of this information is from the "Old Tools Archive"  the rest is from my fallible memory.)
How complete is the information in this table?  There's no way to tell when one has  a "complete" set of Frederick Post catalogs.  Catalogs were issued at irregular intervals and edition numbers were frequently skipped.  For example, the 1903-04 Catalog was the "Fourth Edition" and the the 1910 catalog was the "Tenth Edition"  but it's inconceivable that Post published five catalogs in between.   I'm sure those edition numbers were chosen to agree with the year of publication.  (Post later stopped that kind of tomfoolery; the 18th edition came out in 1936; the 19th in 1949.)   In short, there's no way to know when one has a "complete" set of catalogs.  Catalogs were supplemented with "Price Lists" which came out every year or so.  Price Lists often listed items for sale that were not mentioned in the catalogs.