Controlled Group Vesting

[Guest carsca]

Question regarding controlled group vesting service:

From 1/1/99-12/31/00, Employee A performs 2 years of service for ABC company and earns 2 years of vesting service under the ABC 401(k) Plan.

On 1/1/01 A leaves ABC and is hired by DEF Co., an unrelated employer. A performs two years of service at DEF, under the DEF 401(k) Plan.

On 1/1/02 ABC Plan is merged into XYZ Plan, a plan sponsored by XYZ company, a related employer of ABC.

On 12/31/02, XYZ acquire acquires DEF Co., and the DEF Co. 401(k) Plan.

On 1/1/03 the DEF 401(k) Plan is meged into the XYZ Plan.

Question: How many years of service MUST A be credited with under the XYZ Plan?

I belive the answer is 4 years of service (iow, the XYZ plan must count both DEF and ABC service), but would like confirmation.

Thanks in advance!