There is a hard cap on total bookings under the Diamond guarantee. More than that constitutes the 'wafer-thin mint' of Monty Python fame.

RESTRICTIONS: This guarantee does not apply to a hotel when that hotel becomes overbooked on inventory by 10% or more (meaning, 110% or more of rooms are reserved). For certain hotels within the Hilton Worldwide portfolio, this guarantee does not apply when that hotel becomes overbooked on inventory by 2% or more (meaning, 102% or more of rooms are reserved). Consult with the individual hotel or click here to determine whether the 2% limitation applies. This guarantee also does not apply to any hotel during Extraordinary Demand Dates.

T&Cs, Diamond Elite Membership, #2

http://hhonors1.hilton.com/en_US/hh/terms.do#general