Very interesting flowchart! We should probably add the large bloomer parallel to the Problem class (I suggest using the locomotive's alternative name, the "Lady of the Lake" class, as "problem" might suggest to new players that there is something wrong with it!).
Also, what is the MR 25 class - do you have any sources on that? Where did that suggestion come from? Also, what is the significance of the MR Crampton being in grey?
Finally, are you sure that the LNWR Experiment class is the best representative of the early LNWR compounds, rather than, say, the Great Britain class?
In any event, lovely spreadsheet! Do you plan to do this for carriages, too; and also for non-railway transport?
Edit: By the Midland 25 class, you didn't mean
this, did you? That is actually a renumbered 800 class.