Far be it for Grasshopper to challenge the acknowledged master on wagonology but a few thoughts:
There were 7(?) 3F in 1960 and all had gone by late 1962. Not sure which one I'll be renumbering mine to, but obviously it will have to be a survivor, and have some modellers licence for visiting the Aylesbury area. No doubt someone will tell me the specific gubbins on the Bachmann release relate to ones which were cut up earlier.....!
There's a pic on P13 of Western Steam in Colour (Hugh Ballantyne ISBN 0 7106 0286 3) of ex GWR 3632 on a goods 22Sep62 and the wagon next to the loco seems seriously weathered. Also Western Steam in Colour 2 (same author ISBN 0 7110 1906 1) P.70 taken on 01Jun63. The long rake in the siding going out of bottom RH of picture has wagons 1 and 3 seriously weathered. OK this is 1 year after 3F withdrawal but it didn't happen overnight. I'm nowhere near enough of an expert to know if these are the same sub-type of wagon but think my modellers licence isn't entirely revoked!
3 things which do strike me about this long rake in the siding:
a/ Wagons 1,2, 3 all have solid black panels (is this quite early?)
b/ The rake is very varied in terms of weathering. I'm not sure I'd have the confidence to have this breath of variation in a model as somehow it doesn't look quite right on the layout yet it's plainly here in full living colour.
c/ Wagons 2 and 3 have bright red axle boxes which seem very clean and incongruous (esp wagon 2). What's this all about? Again am not sure it would sit comfortably on a layout yet there it is.
ie I think I CAN have a MODICUM of seriously weathered wagons with 3F as longs as the overall pct remains low?