Bill Welch wrote:

The June issue of MM in the section entitled I think "Miscellaneous"
has a short section on reporting marks and responds to why
some "Private Owner" reporting marks ended in "X" and others did not.
The author contends that at some point this was done to differentiate
those entities that were owned by railroad companies and those that
were not. (I am paraphrasing here) and gives as examples PFE and
SFRD, which were certainly railroad owned.

Peter Weiglin got it wrong, and you got it right, Bill. The date was around 1915, and the existing car lines were grandfathered. Of course, Mr. Hundman dislikes criticism, so a letter to MM pointing this out would run a poor chance of publication.

Tony Thompson Editor, Signature Press, Berkeley, CA
2906 Forest Ave., Berkeley, CA 94705 www.signaturepress.com
(510) 540-6538; fax, (510) 540-1937; e-mail, thompson@...
Publishers of books on railroad history