I'll try to keep this brief, and I realize some may disagree, but I've always wondered why these Victorian copper issues from 1860 - 1894 are treated as distinct types, beyond the historical fact that SCWC chose to separate them. Yes, the portrait changed in 1874, but there are actually 13 different obverse portraits across the 1860–1894 period, along with 14 reverse varieties. When you compare the reference images for the types here, the reverse designs show greater variation (for example, the lighthouse) Yet, the 1874 portrait change is not especially dramatic in comparison.
As Spink notes, Victorian coppers are among the most complex series to study. The same principle applies to the penny. The 1874 change is somewhat more noticeable on the penny, and on the farthing the sinking of the bust is even more pronounced, so I can understand why SCWC treats those separately (although not as a new number, nor why that separation is used here).
Overall, these varieties seem too similar to justify being classified as completely different types. After all, the “aging queen” portrait progression was also applied to Canadian coinage, yet those changes did not necessarily warrant new type distinctions.