If you spend any time at all perusing early poker strategy books, it's hard not to come away with an uncanny feeling that what you're reading sounds very familiar.
Especially if you're a poker player yourself who studied the game seriously, you might well come away from many of these earlier texts thinking the same thought — these guys had a lot of it all sorted out long ago.
That said, there are some elements of these books that mark them as coming from another time.
The generally raised level of discourse alone sets them apart somewhat, as do some of the phrasing and syntax which though highly readable clearly are of an earlier era.