Goodness, I feel like a doof. I had scoured the @font-face code so many times that I became fixated on it, while apparently neglecting the actual call to apply the code. I left out a comma between the primary and secondary font-face values, producing inconsistent results due to broken syntax.
Let it be known—it’s always a good idea to proofread all of one’s code.
I apologize for wasting your time!