Um, the 'announcement' says there will be a 07:40 from Aberystwyth. In that case, unless they are axing one of the earlier morning services from Aberystwyth to Carmarthen there will probably be three vehicles overnight at Aberystwyth and two at Carmarthen. Trying to derive the new timetable from what the 'announcement' says sparks another question, do First cycle vehicles between stabling points or do they always take vehicles back to their home depot every night as Richards Bros seem to do? If my stab at the new timetable is correct, one vehicle that starts the day at Aberystwyth ends it at Carmarthen (and vice-versa).
Well, of course this business of leaving buses at Mid Wales Travel's depot is, as I said, based purely on the word of one driver, so it may well be that three buses would be needed rather than the two that he mentioned. On the other hand, as that announcement mentions an extra late-night service running from Aber to Lampeter, I suppose it's possible that this would leave two buses in Aber and one in Lampeter at the end of each day, with an extra service running from Lampeter to Aber to form the 0740. I'm sure it'll all become clear in the fullness of time.
If First are indeed renting space from MWT as opposed to opening any kind of operation in Aber, I suppose it would make sense for First to, as you say, cycle buses through starting points, making it easier to take each one out of use as required for routine maintenance.
I'm very much enjoying the last sentence of that announcement, that "Since the Arriva pull-out in December last year, the two Councils have been negotiating with more sympathetic suppliers..." - that'll be the supplier that sympathetically pulled out of the X40 and handed it all over to Arriva a few years back, then