Hello Ironwaves,
There is no way to recover text messages prior to the addition of the Recently Deleted section within Messages. You could revert to a backup where they did exist, but doing this may result in the loss of data from now to when the backup was taken.
I'm not sure what you mean by "hidden alerts?" If you silenced notifications for someone, their messages will still appear in the Messages app (when they text you), you just won't receive a notification on arrival.
If the messages aren't in your Messages app or Recently Deleted section, they are unfortunately gone forever. As I said above, them being silenced means nothing. If they text you again they will still appear in the Messages app, but you will not receive a notification. Unfortunately if they do text you, you still cannot recover the old messages.