I recently made a new town using SP 253, and I've been noticing around my game that some families (just a few) have last names that include a leading space. This is confirmed when I use MC > Rename.
I verified that my name list XML doesn't have extra spaces in it.
Has anyone else seen this?

Where did the name come from ? Do you perhaps have sims in your Library that have last names with leading spaces which the immigrant may have inherited ?

The name came from a custom XML mod whose source I can't recall, but I edited it to remove animal names (because I don't have Pets). There are very few Sims in my Library, and the name chosen was not one of them. I searched the XML for the particular name (Ruel), and there seemed to be nothing unusual about it.
Hmm, a thought just occurred to me: If what appears to be a space in the XML is, in fact, some "space-like" entity instead, would that be imported?
My understanding of XML is that any white-space, such as tabs and actual spaces, is ignored outside of quotation marks... but if a "NBSP" or half-space or something is there, would the mod import that?
(I'll have to open it with Notepad++ and turn on display of non-printing characters so I can make sure.)

The mod has actually been trimming whitespace off of custom names since V232, since another user noted the same problem a while back.

That is why I brought up the possibility of a legacy issue where an existing sim in your Library already has that name.

If the issue is a non-whitespace blanking character then, yeah, that will still cause issues, since the mod would indeed import it verbatim. But you should be able to see it in a proper text editor.

I checked this morning, and from what I could see it was a normal space.

Interestingly, a MC search by last name with " " as the first letter did bring up the correct Sim at the top of the list, but the ones listed after that had names beginning with R (no leading space).