Under the "My Purchases" tab the items are listed under two categories "Plugins", and "Themes". Free items will not be listed there, and do not require a license to use, or update. If the dev has removed the plugin, it will no longer be listed, and in turn there is most likely no update anyway. If the plugin has been removed from the store by the moderation team, It is most likely due to issues with the plugin, and again, most likely doesn't have any update available.
Are your missing plugins still listed in the store? If so, you may need to try to contact the dev to see if they can re-issue a license.

OK, yeah; I will have to contact the developers individually for help I guess. I will go and start hunting them down. I have 11 plugins that require keys and they are not listed under "my purchases". All the other ones, I have updated already. I moved my site to a new server, and have been having many issues since. Thanx for your help!

If you get them here's a tip. I copied all of mine into a notepad document, and saved them on my computer just in case.

Yes, I was thinking I should have done that already. Thanks for the reminder (:

Paypal with have the purchases on a statement if the developers need proof of purchase.