150 is the total number of in-production plates which can be actively for sale at any one time, or the total number of potential-new plates in which pre-sale vouchers can be actively for sale at any one time?
Here's the statutory language:
"(b) If the Legislature has approved 150 or more specialty license plates, the department may not make any new specialty license plates available for design or issuance until a sufficient number of plates are discontinued pursuant to s. 320.08056(8) such that the number of plates being issued does not exceed 150. Notwithstanding s. 320.08056(8)(a), the 150-license-plate limit includes license plates above the minimum sales threshold and those exempt from that threshold."