Thanks for this David.
As of today the Bustimes website, corroborated to some extent by my own sightings, identifies eight vehicles now associated with the Kent Country operation -
https://bustimes.org/operators/kent-country/vehicles. Three are the original 477 buses, SEN199-201 (YY14 WDU/V/W), and it appears at least one of these (SE199) has already been called upon as a backup on the 416 on Monday 29 June and on all of 416/417/308 on 30 June and 1 July.
The other five have at least some existing association or have just gained one with GoAhead London, and two of them are yellow SEN36 (YX61 FZV) as you have illustrated, and SE175 (SN12 AUM) which I photographed this morning crossing the bridge approaching Borough Green Station (and then boarded) heading towards Bluewater, a new extension just added by Kent Country commercially to some journeys of 417 and 308 and one return trip on 416, which appear often to be well used.
The other three are SE232/4 (YX15 XMK/M) which are the most recent recipients of green livery, though SE232 at least is not yet fully signwritten, and the newest SEN66 (YX25 OJY) which is plain white and appears to have come from the Carousel fleet within the High Wycombe part of Oxford Bus Company.
The attached advert promising further fleet developments has been posted inside some of the buses currently in use including SE232, but whether the yellow ones will stay remains to be seen, they may just prove to be short term loans pending further arrivals. Another subject where more reports will help to document the story as it develops.
There is also the revival of a traditional name, Green Rover, associated many years ago with London Transport, for a new Kent Country day ticket for £5.50. Perhaps the only snag so far is that there is not yet a Kent Country link between the 477 at Dartford and the other services at Bluewater, for which you currently need to use someone else's service.
Derek J