[Arran]

I don't think it was exactly a mystery that the first household Transitone set was a Simplex designed and built radio, Ron's book explains this, if the dial didn't tell the story the chassis and circuit used would have, Philco did not have any other model in their lineup that had a TRF circuit at that point in time. If you take the example of RCA buying out Victor in 1928, and then allowing the Microsynchronous sets to go into production for 1929-30 then it makes perfect sense. Nine times out of ten a manufacturer will engineer, design, and tool up to produce a new product at least six months in advance, in the case of cars the process starts up to five years in advance, mergers can happen at the drop of a hat, maybe a couple of weeks, so it would be very expensive and foolish to cancel a new product on that basis. You may also notice that the Simplex uses a Philco style "V" patterned grillecloth so either they got that from Philco and continued producing and marketing sets under their own name as well as the Transitone name after the merger, or they used the same supplier.
Regards
Arran