Hi Soo Line..
You asked.."How about a 19/Train Order that granted two trains overlapping authority on a section of Main Track outside Yard Limits? Say, a work/ballast train dumping rock between Romeo and Uniform, able to duck in the clear at Sierra, and a "through train" must head through those limits from Lima to Zulu?"
The Work Extra would have no direction specified thus he would be named "Work Extra 150" meaning he is opposing everyone and would not be able to use Rule 251 to supercede superiority for following movements.
If an Extra were to run over the working area, he would have a copy of the Work Extras running order..the running order would either relieve the Work Extra from flagging or not mention it..forcing the Work Extra to protect against Extras(flag). The Extra would then proceed, if the Work Extra is protecting against Extra's, expecting to find flagmen..if the Work Extra were relieved from protecting against Extra's, the Extra would protect itself by following it's own flagman through the Work Extra's running order limits.
If the "through train" was a superior train, the Work Extra would be ducking in the clear as required by Rule S-87..the "five minute" rule.
By the way..a Work Extra vs. a non- Work Extra are the only type of opposing extra moves that do not require a meet for them to run against each other. If you have any questions on that, let me know and I'll explain what I mean.
Rule 86 required an inferior train to clear the time of a following superior by the superiors time at the station to the rear.
If you would like some in depth Train Order operation info, private message me..I work in territory like that everyday and have spent most of my operating career doing so.
Hope this helped..