I don't know why you think you can't view all the pictures? You can't be sure all the pictures you can't see, are still on the memory card.
It is not much I can go on, but I give it a try.
First, if you are not sure if something happened with your memory card in the came, don't shoot a picture till you have checked the card in an external card reader connected to a computer.
With free software to recover your files on a memory card:
http://www.memorycard.freedatarecoverysoftware.org you can check if some pictures that should be on the memory card are deleted. If the software detects one or more files, it will show you. Then you can try to recover the files.
Other sites you can look for software are :
www.cardrecovery.com
www.wondershare.net with free trail
www.cardrescue.com with free evaluation version
I hope you find what you are looking for.
Could be some software only detects some files (Then you know there is something to recover) but the firm wants mont for a full version. Just try another link.
I got my software in a package with an expensive memory card, so I stopped checking what link worked the best.
Now what could have happened with your photos.
Someone else could have deleted some pictures, because the did not like the pictures. Or in the past year the camera was switched on, while the battery was almost empty. And while accessing the memory, the voltage was too low to write back the correct file system. Some pictures or the pointers to the pictures ware corrupted. That is why it is not allowed to remove the battery, while the camera is accessing the memory. Can be seen when a light is flashing on the camera.
I hope you find your pictures.
