I went through my pictures again. It looks like I received images (different ones) of the same canoe from two different people. Apparently I have images of 4, not 5 canoes that are believed to be SLBC's.
Unlike the other 3, the canoe with the lowest profile is a sponson canoe. I am not sure if that has significance but it should be noted. That canoe also (as far as I can tell) does not bear a WW decal or a SLBC tag.
We may never understand how true to Rushton's builds these canoes were constructed, but if we accept that they were done on his forms, then we should also presume that the stems, inside and outside, were built on specific forms. We know that any change in the shape of the stems affects the height of the stems, lengths and bend of the inside rails and also the shape of the decks.
Assembly of significantly differing components would be a major headache in any kind of volume shop. Examine any builders shop and you will see patterns and forms that are specific to each form. Willets shop cited as an extreme example.
It would not be likely that there would any significant variation presuming the use of the same forms and patterns.
A change of stem height and curve must be very deliberately done. The canoes that were built off of my form in the 1970's would be roughly identical to canoes made from that same form in the 1920's or earlier.
As Michael notes, there were other builders who were producing Rushton like canoes. Many of these used virtually identical components and build techniques. They were also very consistent about marking them with their own names. A Wells or a Brown are marked as such.
Were any of the WW canoes built by other hands? Quite possibly. The contract build that was the norm for Rushton may have continued.
To further complicate this, presuming that we wanted to alter the shape of the stem (and all related parts), it is very possible to "adjust" the form by attaching longer inside rails and then attaching the reshaped stems farther out. This would reduce the curve. Or, you could also alter the form to push the curve out which I suspect is how Brown built the torpedo stemmed Rushton look alike that I own. These are not high volume methods.
It's quite thought provoking.