A) When you fly with an instructor at a club check out (e.g you have let the 28 day rule lapse at your airfield) this is logged as you P1.
Be sure that you both agree that you are logging P1 as you cannot both log P1 time.
B) When you do differences training to a PA28 arrow with variable pitch from a standard PA28 or from a Cessna 150 for example this is logged PUT and logged as it was before you got your licence. You can then get the front of the log book signed up to certify you have had such training if you wish.
C) The only time P1/S (and you log the time in the P1 column) is used is following a siuccessful flight test and the examiner countersigns the entry. PPL skills test/IMC test etc
Suggest this be made a sticky as it seems to get asked about many times.