To be honest @Roberta2 I am a host who shares my home. I don't really notice whether guests provide a surname when they book. I don't think it is compulsory.
I only take guests who have photo ID and a clear profile photo of themselves. I also ask guests vetting questions when they book.
You can certainly add it to your house rules that you only accept guests who provide you with a copy of their passport but obviously you need to be GDPR compliant and it may put some people off from booking with you.
We've had a look in the back end and this doesn't seem to be showing up and is certainly not by design. Could you give me some screenshots or specific areas where this issue is showing so we can get it fixed?