You're right, they don't match. I've known there were at least two variations on the Alpha fin shape for awhile, but I didn't know where they diverged. Now, thanks to that SP-25, I think I do.
That "your first rocket" instruction sheet on JimZ is not from a K-25 Alpha kit but a separate publication. It appears in "The Alpha Book of Model Rocketry", which has a 1972 copyright date in the form available on the Ninfinger site
HERE. It's page 10 of the document.
The rest of the instruction set there matches a set I still have from when I built
my first Alpha in the late 1960s. Notice that the engine mount assemblies are quite a bit different between the first and second appearances of the exploded view on the JimZ site as well.
I matched the SP-25 scan above with an Alpha III fin can and it is just about a perfect match. That surprised me, I have to say.
Current-issue Estes Alpha kits have laser cut fins which are
also that slightly higher span and aspect ratio fin that matches the Alpha III and therefore also what's in the SP-25 rather than the "your first rocket" fin pattern on JimZ different still, and slightly smaller in span and chord.
Interestingly, the laser cut K-25 fins available from Semroc match the "your first rocket" pattern exactly (so my Alpha II clone has that fin shape).
So it appears to me that the divergence came all the way back at the issuance of the K-25 Alpha kit rather than when the Alpha III came out (which is what I had assumed before). Interesting indeed.