Some where I remember seeing error tools but can't remember where it was.

Bought a box of wrenchs today and the stamping doesn't match the openings
on one of the wrenchs. Havn't taken a pic yet but I will.

I have a 1/2  9/16 box end that has the sizes stamped on the wrong ends

Here ya go, there are no other markings on this wrench.
This says 1/2 and I measured it at 13/16.


and this says 9/16 and I think it measured 7/8.

Probably not errors. Most likely the old way of naming the tool by the shaft size of the fastener.
From The Wrenching News- http://www.wrenchingnews.com/wrench-logos/logos-page-1.html

Quote5 - Size Standard Markings
Note: In the United States prior to 1929 the sizes stamped on wrenches usually referred to the diameter of the bolt not the actual opening size. Thus a wrench stamped ½ U. S. would actually have a 7/8" wrench opening size as a nut for a ½" diameter U. S. Standard bolt would measure 13/16" across the flats and allowing for 1/16 clearance would require a 7/8" wrench opening. This same size wrench would also fit nuts for 5/8" hex cap screw and bolt and nuts for 9/16" S.A.E Standard Cap Screws and thus would be marked ½ U.S, 5/8 Hex Cap, and 9/16 SAE. Carl Bolt's website page on tool standards pictures 17 wrenches with 19 different identifications and sizes all marked 1/2"! This could get pretty confusing so circa 1929 the American Engineering Standards Committee specified that wrenches should be marked with the actual width across the flats of the nut or bolt head they would fit
AF    Initials: AF (used with size in inches of nut or bolt head i.e. I/2 AF)
Across Flats (British?)
Size as measured across the flat sides of nut or bolt head or actual wrench opening size
OC    Hex logo and initial C (used with size in inches of bolt diameter i.e. I/2 OC)
Hex Cap Screw
Found on older forged wrenches before 1920 standard want into effect (see note above)
SAE    Initials: SAE (used with size in inches of bolt diameter i.e. I/2 SAE)
Society of Automotive Engineers (fine threaded nuts and bolts)
Found on older forged wrenches before the 1929 standard want into effect (see note above)
USS    Initials: USS (used with size in inches of bolt diameter i.e. I/2 USS)
United States Standard.
Found on older forged wrenches before the 1929 standard want into effect (see note above)

Huh, I didn't know that about the old wrench stampings. Wow, that must have been pretty confusing, back in the day.

Thanks Papaw that really cleared that up.
I bet that old system really screwed people up know wonder they changed it.
Guess I better not have it gold plated :-).