1: Yes
2: There is some moderation but the times generally progress as specific ability is put in place.
3: The plans actually begin to converge and that would be reflected if subsequent, short, SPPs occurred. The S-to-L you see here was set up as a single SPP due to the particular circumstance but would normally follow a substantial GPP and all 400 programs would normally have longer GPP lead-ins, IMO, which would leave somewhat less time in further SPP cycles.
I think you can evaluate all this best with a review of the lactate thread in the archives- that’s a gold mine.