Try some parallel thinking.
The “LMS” 2p, 3f, 4f, 1f (tank), 3f (tank) are all pregrouping.
Similarly, the GWR 14xx is a revamped 517, the 57xx a revamped “large” pannier tank, and the 64xx an updated “small” pannier.
OK so there might have been some small differences but fundamentally Collet realised that the legacy he inherited from Chirchward was extremely strong, and other than a few improvements to details, he was happy to turn a Star into a Castle, etc, and spend his time on more pressing matters such as running the mechanical side of the railway.
The rather more fragmented locomotive development of the LNER and SR might make that a little harder, but have a look and find similar locos.
That said, I am hoping to one day have LNWR sounds from the coal tank produced by Paul Chetter (I like what he has done with the rest of the programming on Zimo decoders) but I am happy to use something which had similar prototype dimensions for inside cylinders, and I have a J94 sound decoder awaiting fitting. If a coal tank file appears later, I can always send the decoder to Digitrains for a reblow.