I think you might be on the 5-year cycle for individually designed plans for two reasons.
Section 12.01(3) of Rev. Proc. 2005-16 states that "until issuance of the official opinion or advisory letter no reliance exists." This is consistent with the IRS' position in the past that a plan signed before the opinion/advisory letter is issued is individually designed. Stated again in Section 19.03(2) of Rev. Proc. 2005-16 states: "an adopting employer has no reliance if the employer's adoption of the plan precedes the issuance of an opinion or advisory letter for the plan". Since your employer adopted a plan before the opinion letter was issued, the plan is individually designed.
Second, a prototype becomes individually designed when it is amended to include language which is not one of the pre-approved options. Since the adoption agreement was amended to include a matching formula which was not one of the pre-approved options, the plan is individually designed.
I would treat the plan as individually designed. If the employer intends to adopt the EGTRRA-approved version of this plan once the opinion letter is issued, I would have them sign Form 8905 before the end of their 5-year remedial amendment cycle in Rev. Proc. 2005-66.