I made challah dough and it was still sticky after 9 cups of AP flour
I have conflicting experience to @Benjamin. I often add a little extra starch to my bread actually, specifically potato starch or sweet rice flour. While all starches gelatinize a little differently, I would not expect you to have any issue shaping the bread, or with rise. What I would expect is a little extra chewiness to the crust and perhaps a bouncy quality to the interior, and maybe a tighter crumb with finer bubbles. The first time I added starch to a bread as an experiment (and far more proportionately), I joked that I had successfully invented storebought bread at home, because that's what the texture reminded me of. That said, I would not expect the textural differences to be huge in your case because you added very little.
Since percentages and math are on the table (I'm sorry but I love math), let's break down the amount of gluten and starch in here.
The recipe calls for 9 cups of flour total, and there are 16 Tablespoons in a cup. So how much gluten is in one of those cups? If we say it's ~12% (I asked Google), then in one cup of flour, there are about 1.92 T gluten, and about 14.08 T starch. If you round, that means about 2 T gluten, 14 T starch. That's a proportion of 1:7.... and I'm rounding up the gluten.
So what difference does a few tablespoons of corn starch make, proportionately? Well, for every T of corn starch you added instead of AP, you were missing one-seventh of a Tablespoon of gluten, or less than a half-tsp, but more than a quarter-tsp. And that amount counts up with every T you added. So, if you added a quarter-cup of corn starch, then you're &quot;missing&quot; almost 2 teaspoons of gluten. If you added a whole half cup, you're missing a little over a Tablespoon of it. But again, we rounded the gluten up before, so... you aren't even missing that much. This is an overestimation.
In the recipe as a whole, you have 144 T in those 9 cups of flour. That means you have 17.3 T of gluten total, and 126.7 T starch. Even if you added the whole half-cup of corn starch, changing the amount of starch to 134.7 and the total amount of &quot;flour&quot; to 152 T.... You've only changed your gluten content from 12% to 11.4%, which would still be within range for all-purpose. Some brands have higher gluten. Some have less. King Arthur brand's all-purpose flour has as much gluten as some other brand's bread flours. And again... I'm assuming you added significantly more than a few tablespoons. That drop from 12% to 11.4% represents a worst-case scenario.
So while there will be a difference, I'm guessing it will be subtle, maybe even undetectable if you aren't looking for it.
One thing I noticed reading the recipe is that they don't call for resting the dough. A short rest (often called &quot;autolyse&quot;) after adding, say, two-thirds of the total amount of flour will give the flour a chance to hydrate and soak up some more moisture. That way, it will require a little less flour to get a workable dough, and your final product will be just a little softer and moister as a result. IF you make this recipe again, it might be helpful.
I'll be curious to hear how your experiment turns out (hopefully okay!)