Looking at
EMR's timetable for this week - there are more HSTs marked than just the 2 diagrams previously mentioned - some of those will be the short sets but it does seem like there's a fair few sets about.
Some 222s will be stopped for maintenance, but equally the HSTs are available and can effectively be run into the ground - there's little point in not using them until they run out of miles. I'd also suggest that PRM compliance is of little importance right now as the handful of people still using the trains are more likely to be able bodied than not