I found a definition for NPRO in the IBM Dictionary of Printing:
nonprocess runout (NPRO). (1) An operation that moves paper or forms through the
paper line or forms path without printing. (2) The process of removing the last
few sheets of a job that is finished printing on a continuous-forms printer.
Normally the last sheets of a job remain in the printer and are forced out by
the next job. This procedure saves time when printing is continuous, but when
there is a delay between jobs, it is necessary to remove the end of the last
job. After the time specified in seconds by the NPRO parameter, the printer
clears out the last sheets. (3) In architecture, an operation that moves sheets
of physical media through the printer without printing on them. This operation
is used to stack the last printed sheet.
I think definition (2) is relevant here. A "non-process-run-out" value of true
indicates that the printer should flush the end of the last job before shutting
down.
-Carl