[Arran]

It's not exactly a mid year change, the code numbers I mean. You see Philco used to design different versions of the same model chassis to accommodate whatever parts they could accumulate from the various suppliers they used. In the post war period there were a number of parts shortages, so some sets, like the Philco 46-1201, could have as many as eight different code numbers, and three or more production run versions, or the same set, swapping everything from tube lineups, to what shape speaker they used. They could swap back and forth between producing different Code numbered versions depending on what parts they could get and what they were running out of.
  I have three Hippo models, one good one, and two project ones, one is more of a parts set. The first one I got has a tuned RF amplifier stage,
and uses a 7A8 octode mixer oscillator, the other two have a 14AF7 twin triode mixer-oscillator, and two IF amplifier tubes. I can't tell you what year these were built because Philco Products of Canada Ltd. used two digit model numbers like the late 1920s and early 30s sets did, rather then a model year prefix like 41-, 46-, etc. But if the Toronto plant was swapping parts around like this you can bet that the U.S plants were.
Regards
Arran