For what it is worth, I just used your method to test an individual packet of Red Star active dry yeast with a "best if used by' date of Oct 2014, which has been in my freezer for 5.5 years. According to your method - plus my eyes, nose, and taste buds - checking after 10 and 20 minutes, it is still good!
Purchased at the same time, is a jar of active dry yeast that I had opened and used, sealed tightly and kept in the freezer. A visual inspection revealed no change in appearance and, no change in smell was detected. That given, I am going to assume it also is fine. The proof will be in the baking, I suppose.

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