That topic has come up here a couple of times on the list.
A nice example is illustrated here:
https://goscf.com/t/38447&whichpage=5and a couple more were discussed here:
https://goscf.com/t/45815The guy offering the double variety on
ebay is a golddigger who way over values any efo item he comes close to having. The candle flame variety is a printing flaw (plate wiping) and nothing major from a production standpoint. Brookman discusses it a bit in the third volume of his work on 19th century (available online for free access at the USPCS website). Scott does not list items like that.