A few other changes I've noticed since earlier in the summer on Bluestar, having been out of the area for a couple of months.
The 1 seems to have reverted to being mostly self-contained, with its own branded E400s operating almost all journeys: in the past 12 months or so (maybe longer) there were one or two diagrams where the 1 and 2 swapped over. The 1710 out of Southampton was one which featured an older bus regularly earlier in the year, and it had been working 2s most of the day. Presumably there was a driver hours reason for the former swap-around.
The 1755 out of Southampton is still the exception, regularly operated with an older bus - I think this comes off the short working from Asda which arrives around 1730, but need to check.
The 20 seems to be more of a random mix of vehicles: formerly purely E200s on Mon-Fri school term times, it now features other "import" single deckers and a couple (?) of the diagrams have gone over to double deckers, presumably those which include particularly busy journeys at some point in the day. It also had the "more" vehicle (260) three days this week, but not on the same diagram.
I believe that a sixth vehicle has been introduced to the route in the evening peak to allow the off-peak 15-min frequency to be maintained, presumably off a school or college service (haven't checked bustimes yet to find out).
The 19 also features additional vehicles in the evening peak, indeed (and this is a rarity these days) actually sees a frequency uplift eastbound for a time in the evening peak.
Not so good is the increased "traffic lag" in the evening peak on the 9, which loses 20 mins or so (00/30 to 20/50, IIRC). Looks like they could do with introducing an extra vehicle off a school or college working on this route, too.
Finally, Empress Road and Eastleigh seem to have given up on showing working numbers on the front of the buses. Totton still do, however.