The 1846/5-O $10 overdate has been discredited by Q. David Bowers and Mark Borckardt (see the Bowers & Merena sale of the Harry W. Bass, Jr. Collection in 10/1999, lot 1360). However, PCGS still recognizes it as a minor variety because there is definitely something in the loop of the 6. To indicate that the overdate is in question, PCGS has placed the 5 in single quotation marks as follow: 1846/'5-O.
Doug Winter identified four different die varieties for the 1846-O $10s, two of which he lists as so-called overdates, one being Breen-6875 (Encyclopedia), the other unnumbered. The image shown above indicates the criteria PCGS uses to identify this unusual variety.