Prepatch Engraved books can only add 1 line of extra mods.
So whatever the mod directly under the top engravement is, is the fake mod. The following mods under those are what the real mods are.
Players were able to word wrap using ascii characters or asian characters to overflow the text to the second line.
These books are rare and are not illegal as well. They are about as rare as any other novelty item such as HTML bracelets of binding or such.
A patch was implemented a while back that shortened the amount of text you could engrave with to eliminate the possibility of players scamming with fake modded books.
These items are legal to own, sell, and trade so long as the seller isn't trying to pass the top mod off as real.
I was the one who stumbled across this bug and reported it back in the day which ironically enough actually got fixed before dupes got fixed. I got a handful of these left with random novelty mods and have been offered a pretty penny for some of them that say 100lrc, 9999 mana, or 9000 hp inc etc... there were also more comical ones like gm slayers, or cow tipping +100 etc.. which tend to sell better than normal looking mods.