PCS must not look back, however, I'm not sure where the reference is.

Another time PCS is blind (PCS doesn't look forward) is for REG to RES. A nice play with 3-99-5 could be:

PBS for Period 2

Bid period 1 | Bid Period 2
OFF OFF WORK | LC LC X LC LC LC etc... (if you make this a long enough stretch, 30/168 will force additional rest, likely 30 hrs starting at 1800 on LC day 2)

PCS (preferably during the 20th 0700):
drop(or swap) the turn on last day of bid period 1. Result:
OFF OFF OFF | LC LC X LC LC LC etc...

This orphans 2 LC days. Earliest assignment is 1800 on day 1 (going REG to RES). Only 30 hours of availability over two days of work (possibly only 24)! Practically unusable for those first 2 days / a nice SC countermeasure.

As for RES to RES, I'd love if Frank could elaborate on the X-day move that orphans LC days; I'm always looking for a new trick.