While this is technically a correct abbreviation, I am not sure it's used in real life outside of print... and like, addressing envelopes at that.

I have never heard anybody speak 'col.' in my life in the way I have heard 'Mr.' If it shows up in dialogue it may be a charge, or if not a charge just a nonsensical error.

Also, unlike 'Mr.' it's kind of annoying and not in wide use. If you can't charge it as an error, I'd charge for annoying the agents.

Is that not common practice for military titles? If I were writing a story with military characters, I would definitely use them, with the possible exceptions of "Capt." and "Cmdr.". I'd say it's equivalent to using "Mr." instead of "Mister/Master" or "Mssrs." for "Messieurs" à la the Marauders.

But maybe I'm wrong and standard practice is to write out the full title, in which case I don't really know.

My instinct is to say that if it's that consistent it represents a conscious choice rather than an error. In my opinion, even if it deviates from standard practice, it's not "wrong", per se. I guess I would ask if they do it for other military titles, if any appear. If so, then I think it's fine as long as the fic is internally consistent. If not, then maybe you've got something for inconsistency, but...

Regards,
Lleu