No, but there is no advantage to keeping them.
The Princess is a disguise, and if you are fooled, you can still enter the castle by solving the puzzle door. If you click the door, you enter the final battle immediately.
(see related question)
Go to the Mordred Museum. Under the bed on the second floor is the missing journal page, with the coordinates to the Pewter Moon.
There are two messages: the Princess note in the Maid's room (castle first floor left) and the note in the Princess's room in the separate tower. Both should go into your item bag.
If you follow the coordinates that the Queen gives you, there should be planets at those locations. The knights are on those planets (jungle, ice, and fire) and each has one of the Mystical Weapons for you to use. Jungle Planet : X-15 Y-15 Ice Planet : X-73 Y-83 Fire Planet X-83 Y-20
This means you have already completed the Arturus part of Astro Knights Island. Your spaceship should be parked on top of the castle if you return to the planet.
x 56 y 52
The crystal gate, and its Golden Key, are on the giant asteroid at X-11 Y-82 in the asteroid belt. You should only go there when you have defeated the three planets (jungle, ice, and fire) and have all three of the space knights with you. Drawing out the Golden Key opens the portal to the other galaxy, where the Princess is being held.
When you defeat all the planets in astro knights island you go to the coordinates X-12, Y-83 ten there should be a giant asteroid retrieve the key from that planet and a portal will appear go in the portal and you will see the "princess" but it's a trick it's really Mordred. HOPE THAT ANSWERS YOUR QUESTION
really all you have to do is read them they should help a little bit the island
your spaceship should be on top of the castle..
Go to the Ice planet. There should be a string hanging out of the wall . pull the srting and you should have the stone (P.S. The string is BROWN)
Take the Princess message from the Maid's room in the castle, and talk to the girl in the upper part of the Mill. She will give you the "cosmic symbols" card. Go to the fountain plaque and click the ringed planet, the crescent moon, the star, and then the sun. It should open the secret passageway.
On Astro Knights Island, you wait for a platform to come down to a level so that you can jump onto it. However, the 6th platform never gets lower than the 5th, so you should jump when both platforms are moving rapidly down. The 6th platform should fall right under you.