Waits' Compendium Errata and Addendum
A very useful resource is A Safety Razor Compendium by Robert K. Waits.
I have v1.2 and have found the following mistakes or inaccuracies.
I you find other problems in this great book, let me know and I'll add them here.
Introduction
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Page vi 
The term “safety razor” was not coined by the Kampfe brothers. See my research here.
Razors by brand
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Brandt 
Patent number is 807172, not 802172 -
Coronia 
Patent number is 775379, not 775397 -
Firm Blade 
“Uses one-half of a split Gillette-type double-edge blade” No, it doesn't. Won't fit. -
Fonta 
“Wrexham, Wales, England” — Wales is not part of England. There are several patents:
GB597918 ― 1948-02-05
GB640185 ― 1950-07-12
CH279397 ― 1951-11-30
CH279398 ― 1951-11-30
GB672947 ― 1952-05-28
GB672948 ― 1952-05-28
GB690828 ― 1953-04-29 -
Gravin Heat Shaver 
Patent is US2324148 Moses M. Gravin - 13 July 1943 -
Hohlraum Rasier-Gerät 
The name is Hohlraum with an h in the middle. -
Krisp 
26355 is patent GB190826355 2168 is patent GB190902168 “Circa 1919” is ten years later than the patents -
Rally Roller Shaver 
Inventor name is: Jonas Åke Gregorius Malmberg German patent: DE830305 US Patent: US2637902 Also, there is no such place as “Esjukstuna” in Sweden, but razors were manufactured in “Eskilstuna” (e.g. Heljestrand). -
Schrägschnitt Hohlraum-Rasier-Gerät 
The name is Hohlraum with an h in the middle. .
Also, the location is Bollwerk, not Boliwerk. -
SENCA 
Patent is by Philip (not Peter) H. Unsinger -
Supramat 
378772 is 378722 and refers to Swiss patent CH378722 -
Ucan 
The patent is US1332587 -
Wanie Rollband Blades 
The patent number should be 608066
A.S.R., Ever-Ready, Star
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1933-34 The last U.S. ‘Ever-Ready’ razor? Razor marked GEM. 
The box is correct, but the razor is wrong.
That's why it is marked GEM.
Here are images of the correct razor:
Image by jmudrick
Image by jmudrick