I've been heavily researching these for several months now.......
Like you said, the text box on the reverse is one indicator, but there is another much less obvious characteristic that should be present on the reverse.....
If you'll post a better picture or scan, we'll have a better guess....Can't tell much at all from the posted image.
A lot of people got ripped off in the 70s and 80s with singles cut from counterfeit sheets, so some ideas are likely conspiracy theories. The fact that PSA holdered blue ones from the 70s and fake black and white sheet singles from the 70s didn't help the theories. They were only produced for a week, but we are talking about Babe Ruth in 1928, a year after his awesome '27 season. He was huge! It's reasonable to assume this made their survival rate more likely.
The factory singles could be returned for a premium and an uncut sheet. There are not many of either. It's not likely someone sent their set of singles in for a sheet and subsequently cut the sheet into singles, so any single with uncut sheet characteristics is fake.
These are authentic:
The two lying horizontal are c.1970s fakes:
[IMG]
[/IMG]
Repli-cards fluoresce purple with a black light.
Ice cream is a dull color under a black light. I have a '28 Fro Joy Tunney with very similar stains, last image. Imagine having a cone with dripping ice cream and scraping the side of the cone with the card that came in the pack.
A repli-card with manufactured aging sold for more than 100.00 recently, and the seller stated it was a reprint in the listing! The buyer could have bought a full set of repli-cards for less than ten dollars!