dynamed seems to suggest the terms are interchangeable. I did come across this: https://www.acog.org/clinical/clinical-guidance/obstetric-care-consensus/articles/2014/03/safe-prevention-of-the-primary-cesarean-delivery but it’s not clearly differentiating as two distinct things, to me it reads more like a change in choice of wording, based on the info available.
hmm - UTD (doesn’t need an account to view the relevant bit) UpToDate suggests protracted for active, prolonged for latent (second stage, as you state). Not much in it, but approving on balance (as if they are interchangeable, no harm in learning it in the way supported by UTD)