Very possible that it is, but I would guess that the answer is no. It sounds like it might have not transferred all the pictures but thought it did. If you have the option set of "delete after transfer" checked, it would explain this problem.
If you have not taken any pictures since the transfer, you can check the memory card for deleted files. If you have taken new ones since, then there is a possibility you have overwritten the ones you are looking for.
The program I use to undelete files that have been deleted from the recycle bin is free and can be downloaded from the following link.http://www.softpedia.com/get/System/Back-Up-and-Recovery/Restoration.shtml
But you will need to put your camera memory card into a card reader rather than using your camera to do the transfer. I would also check your C: drive for deleted files.
Another suggestion is to do a search of your entire hard drive for ".jpg" or the file extension your pictures are taken in.
Hope this helps.