Makes sense to me.
The only reason I have cream of tartar in the cupboard is to make snickerdoodle’s. I don’t think I’ve ever seen another recipe that called for it.
Meringue. Almost every meringue recipe calls for it.
Now that you mention it, I have never made a meringue.
We know what you’re doing this weekend.
Oh wow, that makes a mess if you try to print it. The Penzeys one prints nicely.
Annnd, they are almost the same recipe. Same amounts of flour, far, sugar. The penzeys recipe uses all butter and makes up for that with a lot more leavening, so i went with that one. Penzeys also calls for less salt (it probably assumed salted butter, and maybe i should have added a touch more) and less vanilla (optional 1tsp vs. 2 tsps).
The last tray is in the oven, and quality control says they are good. 
I made just shy of 60 cookies
I’m not sure what issue you had, but I just tried it and it printed up fine for me. I used the “print” button on the page. Fits on one sheet of paper, double sided.
Anyway, Penzey’s is always dependable, so I’m sure they’ll be great, too. Like you said, recipe’s pretty darned similar. I don’t think there’s really that much variation with the basic snickerdoodle recipe. Fingers crossed. Good luck! (ETA: Oh, I see they’re already done. Sounds like a success!)
Yup, taking a few leftovers home, but about 45 were eaten tonight. A friend brought his fabulous shortbread cookies, there were brownies, mocha donuts, and some other snacks. So they were pretty competitive.
I ended up cooking each tray separately, because they took 8 minutes to cook, and it took about 7 minutes to ready the next tray. 
When i tried to print it, i got big spaces where the ads had been. (I, also, used the “print” button.) I was able to rearrange the interesting parts in Acrobat and printed the recipe on one page, but i think I’ll stick with the Penzeys version. Really, the only difference is replacing some shortening with butter and adding more leavening. And Penzeys suggests you make a lot of cinnamon sugar and have leftover, instead of making just enough.