Slightly off topic, but here's a story about part subs
In the world of Kenmore washer agitators, there have been something like 8 or 10 different agitators in the original belt-drive models, but there were literally perhaps 100 different part numbers for these agitators. Tiny revisions like the addition of the "mini-fins" on the original Penta-Swirls gave the P.S. a new part number, as did a change in color from gold to white. As well, there were several changes made to the polypropylene Super Roto-Swirl, one to the sealing surface at the agitator cap, and a couple changes to the centerpost of the agitator on the underneath side. These changes caused new parts numbers to be made as well, but in these cases, the old parts all subbed over to the newest version available.
Currently, even the handful of different Straight-Vane agitator part numbers sub-over to the final version of the Roto-Swirl, so that the legions of S.V. equipped machines will still show as having an agitator available if a customer so desires.
One case where Whirlpool goofed, as I mentioned above, involves the two generations of the Penta-Vane. This agitator came out in 1973 in the original gold color. It was usable with or without an extension for the softener dispenser, and this agitator continued unchanged until summer 1981, even in gold.
In 1981, a new version of this was engineered to be white, and it had two changes made to basic agitator. First, a weep hole for air bubbles was added to the agitator skirt. Second, the little fins underneath were added to be used with the basket-mounted filter models. Other than the color, the agitator was otherwise identical to the original. When the original gold version was finally out of stock, it should have subbed over to the white version, but it never was. Thus, some poor Johnny Q Customer somewhere probably went shopping for an agitator for his 197x Kenmore with Penta-Vane and came up empty, when the white versions were on shelves and still available.
The changes in the Roto-Swirl and Straight-Vane were much more significant than these two Penta-Vanes, but those agitators subbed, whereas the P.V. didn't. Clearly, this seems like an oversight by Whirlpool as these two agitators fit in any large capacity machine from 1973 on with no issue.
I am not saying that WP royally screwed up, but this is how oversights can happen, and I think that may have happened with the compact dryer's blower wheel as well. A test of the new blower in an older model would be a fun project.
Gordon