Remember that the full name of the third ship was KENNETH A J MACKENZIE not simply A J MACKENZIE.
I don’t think you have done anything wrong in your searches. I have queried Ancestry.com myself and find the same issues you have encountered. Here is a partial or possible explanation.
Both NIRA LUCKENBACH and KENNETH A J MACKENZIE served for at least part and perhaps all of their wartime careers in the Pacific Theater. KENNETH A J MACKENZIE was constructed at a shipyard in Portland, Oregon, and it was very typical for West Coast-built ships subsequently to operate in the Pacific. (As I mentioned in an earlier e-mail, NINA LUCKENBACH was built on the East Coast in 1919, and she eventually must have found her way to the Pacific in time for World War II.) My extensive and frustrating experience with Ancestry.com is that crew lists for ships operating in the Pacific and Indian Oceans almost never include Armed Guard sailors and officers, even though I am certain Armed Guard units were aboard these ships. By contrast, crew lists of ships operating in the Atlantic, Mediterranean and Caribbean generally do include Armed Guard personnel when aboard those ships. I do not understand this discrepancy. It’s true that Armed Guard personnel were not “crew” in the sense of the merchant marine crew aboard merchant ships but their presence aboard ship should have resulted in their inclusion on crew lists, as was true in most other cases as just noted.
The above explanation does not hold for BOOKER T. WASHINGTON. As best I can determine, this ship operated extensively in voyages to and from the Mediterranean plus several North Atlantic voyages and at least one to the Caribbean. In a few cases I found lists of Armed Guard personnel appended to or included in the merchant marine crew lists – but never listing your uncle. And in several instances, I found crew lists for BOOKER T. WASHINGTON that did not include Armed Guard personnel even though I am certain that an Armed Guard detachment would have been aboard. I have no explanation for the latter.
Gazing into my crystal ball, I can theorize that your uncle served in NIRA LUCKENBACH and KENNETH A J MACKENZIE on Pacific voyages, for which Armed Guard personnel were not included in the crew lists, for whatever reason. And then he had the misfortune, for your purposes, of being aboard BOOKER T. WASHINGTON for one or more of her voyages for which, unaccountably, there is no mention of an Armed Guard detachment. There may be other explanations but this seems possible or even likely.
I don’t know of course your exact interest in researching your uncle’s Armed Guard service. One option to obtain more information and possibly to pinpoint any specific information you are seeking is to request a copy of your uncle's official military service record, which ideally but not necessarily always would provide a substantial degree of detail about his wartime service, such as the ships to which he was assigned, applicable dates, training, illnesses or injuries, any decorations or medals earned, etc.
See this page within the Armed Guard websit, http://armed-guard.com/searchmil.html, specifically section II.A.1 - Records of Individuals, Military. You will have to contact the National Personnel Records Center in St. Louis, MO, and provide as much identifying information as you have. The page has links to all the information you will need to request his records, including a required form. There will be a fee involved for research, photocopying and mailing but the Records Center staff will alert you to the cost before beginning work.
Note, however, that someone such as yourself, who is not next of kin to your uncle, may not be able to obtain his complete service record. (Next of kin in this context = parent, spouse, sibling, child.) If there is someone still living in your family who is next of kin to your uncle, presumably a grandparent, mother/father, aunt/uncle or first cousin, it would be best if that person submitted the request for your uncle’s record. You can do the legwork of research, completing forms and otherwise preparing the request but the request should be signed by that person. If there is no longer a person who is next of kin still living, then make the request yourself and hope for the best. At worst you will still get a large portion of his record. What you may not receive will be medical information or disciplinary information, if such exists.
Your uncle was a brave man; they all were.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website