Don't know if it's still the same way but prior to the first PCS run after you submit a slip, you were always last in line for the award. Commencing on the second PCS run after submission is when you get put in seniority order. That's why it's better to modify a request than delete it and start over. The same thing happens to a modification but at least the original is still in for consideration. Don't know if it's still this way.
Denny