extraneous object added with every library asset (Illustrator)

Early on in my experiments with the Illustrator CC library, I added a few common items including a piece of text with a copyright statement. Many months later, I'm adding more vector art assets to other libraries, and I find that same copyright text snippet showing up in every asset, positioned several inches below the artboard of the added object. I'm puzzled where it came from, because it was never present in the documents from which I'm adding artwork. In fact, it's a 2017 copyright statement that I've not used for a long, long time!

I've tried different methods of adding the art, but the mystery text object always appears. I can, of course, edit each one and manually delete the extraneous point text object, but the art objects themselves are small (about a pica square) so the regenerated thumbnail comes in only a few pixels wide/high, which is often too small to distinguish one artwork from another.

Is there anything I can do to prevent this rogue text object from inserting itself into every asset I save?

😕😕

I asked earlier in the Illustrator forum, and was encouraged to ask here.