There are other examples of this:
Palant’r of Elostirion -- Unique. Palant’r. Playable at The White Towers. Discard if the bearer moves. If the bearer is a sage: your hand size increases by one and the bearer is able to use this Palant’r this turn if he taps. With its bearer able to use a Palant’r, tap Palant’r of Elostirion to draw a card. Bearer then makes a corruption check
Pallando -- Unique. His controlling player may keep one more card than normal in his hand. Opponent must discard his cards face-up.
Emerald of the Mariner -- Unique. Hoard item. Bearer receives +1 to all of his corruption checks. Controlling player may keep one more card than normal in his hand. This item gives zero corruption points.
Elrond, Cirdan, Galadriel, the Lieutenants, Shifter of Hues and The Lidless Eye all say you may keep one more card than normal. That seems to be the standard phrase. However, the Palantir and the book increase hand size. [Are there other cards that say this?]
A literal reading seems to imply that multiple cards that say you may keep one more card than normal only allow you to keep 9 cards. However, that's certainly not how it is played. I haven't done a search of the digests yet, so maybe there is something in there that addresses this question.