(b) For the purpose of determining a person’s eligibility to participate in an approved program where the person’s county of residence establishes a program with another county or contracts for services pursuant to subdivision (a), the following eligibility requirements shall apply:

1. (1) Where two or more counties jointly establish a program pursuant to Section 11796 of this code or Article 1 (commencing with Section 6500) of Chapter 5 of Division 7 of Title 1 of the Government Code, subdivision (b) of Section 11838.2 shall apply.

2. (2) Where a county contracts for program services from another county, only those residents alleged to have committed a violation of Section 23152 or 23153 of the Vehicle Code on or after the date their county of residence executes a contract pursuant to subdivision (a) to provide program services to their residents shall be eligible to participate in such approved program pursuant to Section 11837.2.

   Counties which contract for services pursuant to subdivision (a) of this section shall notify the department not later than 14 days following such action.