As used in this chapter, the date a firearm is an assault weapon is the earliest of the following:

1. (a) The effective date of an amendment to Section 30510 or to former Section 12276 that adds the designation of the specified firearm.
2. (b) The effective date of the list promulgated pursuant to former Section 12276.5, as that section read in Section 3 of Chapter 954 of the Statutes of 1991, which adds or changes the designation of the specified firearm.
3. (c) January 1, 2000, which was the operative date of former Section 12276.1, as enacted by Section 7 of Chapter 129 of the Statutes of 1999.