Thanks everyone for the support and replies, and I'm sorry about my apparent misuse of the forum and poor forum etiquette. This was not my intent. When I created the thread, I thought I had checked the box to receive notification emails when replies were posted. I guess I didn't after all. When I didn't get any emails, I just didn't check back until the weekend. Apologies.
To clarify one detail, these are OEM blades that are original to the deck. They've been taken off and remounted a number of times for sharpening, cleaning and routine maintenance.
The solution to the issue I encountered was as simple as this. The spindle has a shoulder that the blade rests on, as others have said. The bolt simply holds the blade to the shoulder.
In the relationship between the hole in the blade and the spindle shoulder, there is maybe 1/8" of slack or "wobble". I took the blades off and put them back on and there was no issue. Then I loosened the two outer blades and pulled them each toward the center blade and tightened them down. When I did this "on purpose", I was able to re-create the issue. So my problem was a product of misaligned variables and just going too fast. I brought the question here because I thought there could be a problem much bigger than that.
Hopefully this thread will help someone in the future. And again thanks everyone for the replies.
View attachment 549123