On the call they specifically indicated it was a one-time royalty rate adjustment.
Not exactly—on the CC, they stated that the new royalty rate could not go back down to the old rate; they did not, however, say whether the rate could go up. My supposition is that it can’t.
However, the royalty rate is still tiered (ie, each tier has been increased such that the lowest tier moved from high single digits to low double digits).
I do not understand what you mean. The tiers that Craig Wheeler referred to on the CC are the old royalty rate and the new royalty rate. At any given time, there is only one rate that is operative, so this is not a tiered schedule in the usual sense of the word.