Thanks Tamyka. The “(Guest Post)” addition is fine with me (but Rachel’s is missing it, FYI). As for the numbering, any option is fine really, although at this point it would be a bit of a hassle for you to include the guest posts in your main series’ numbering, since you’d have to re-number LWTM #17 and onward. So I think either leave them unnumbered or go with e.g. “(guest post #4).”
If you’re really going to plunge into regular guest writers going forward (I’m not sure that you are), the other option would be to require guest writers to use the standard title and numbering e.g. “last week, this morning #31”. You wouldn’t even necessarily need the “guest posts” label in my opinion, since that would be pretty obvious. Or you could slap on a little editor’s intro on the top of each guest post introducing the person and their post.
Okay, submitting… :)