I don't have the cars (they were wrecked). I don't have the Marti report (never had a need for it). I don't have the order sheet (I wish I did). But I have the door data plates, well 2 of them.
The back story is there was a special order that was made in district 72 for a non-standard paint color - "Salmon" for 1968 Mustangs (apparently Hardtops only). I got this information decades ago.
Here are two door data plates, the front, and the back - reversed (using my Photoshop software) so you can read it.
OK, what do you see?
Skip down to the DSO entry. It is a definite 72 - San Jose (that district still located in California). Then a four digit number, which has been defined as the order number FOR THAT DISTRICT. It is merely a sheet of paper that says to paint the cars "Salmon", maybe some other stuff too, but whatever was done to a Mustang, with DSO 72, and code 1191, is on that sheet of paper. That code, 1191, has been documented as Salmon paint, and you can see that Salmon paint on the back of the door data plate on the ends.
Don't try read anything else into a DSO with 6 characters (no special decoder ring was used) and there may be a letter in there somewhere.
PTO may mean PainT Order, don't try to read anything else into a DSO with 6 characters.
Jim