I seem to recall seeing something about not being able to look at the second card, been a while since I saw the rules.
I think it has to do with adding some semblance of "seamanship" to the game. In the Wings of "whichever" aircraft game, you were not supposed to look at the other maneuver cards.
It does make the game interesting and is one of the easiest house rules to implement either way.
Nothing in the rules prohibiting looking at your preplanned card to refresh your memory (just checked to make sure I remember it correctly!). You may be thinking of not being allowed to check the ships attitude to the wind before planning the second card.
In Wings of War/Glory WWI you plot all the cards at the same time so no need to check them again. Not sure about the WWII game.