If it's absolutely not on the label I'd limit yearly applications to 2 or 3 at the most. Any more than that would seem to be excessive, and would indicate that 2,4dB obviously isn't working for the kind of weeds that you are trying to kill. I'd strongly advise you to check out using Thunder herbicide at 4 oz per acre available Daniel's farm store for $189 a gallon. This product sounds pricey, but is actually cheaper per acre, replaces both Clethodim and Butyrac 200 so you only make one pass for all of your weeds. Thunder herbicide has a residual effect and will clean up tough weeds that your other herbicide won't, and you will be amazed by how clean your clover looks. Spray when the weeds are 3" high or mow before spraying.