I have suddenly lost some of my drafts on Mozilla Thunderbird, where might they be please?

Try searching for a folder named 'Outbox' - I've found they can end up in there under certain circumstances.

 

This folder could appear anywhere, so if you have a complicated multi account setup it might not be so visible - I found a few old 'missing' emails going back years in mine when I discovered it for the first time!

 

I have now noticed down in the bottom right hand corner it's stating Unread: 13 (showing) Total: 20.

How can I opened to view the remaining 7 please?

Perhaps you have filtered the view to show only unread messages?

View => Threads => All (maybe a bit different labels, my Thunderbird is Danish)

9 hours ago, up2you2 said:

I have now noticed down in the bottom right hand corner it's stating Unread: 13 (showing) Total: 20.

How can I opened to view the remaining 7 please?

Brilliant - thanks a million, I live in Thailand and I want to give you a coconut.

Going to View, Threads, trying out some of the options, then reverting back to All, this is in fact what did it.
So happy but what's more so relieved.