Can someone please help me calculate the vesting in the following situation?

Plan changes from calculating vesting based on Plan Year/1000 hrs to elapsed time effective 10/1/02.

Participant was hired 2/1/00, terminated 12/31/03. Are the vesting compuation periods as follows??

1/1/00 to 12/31/00 - Worked 1000 hrs - credit 1 YOS
1/1/01 to 12/31/01 - Worked 1000 hrs - credit 1 YOS
1/1/02 to 12/31/02 - Worked 1000 hrs - credit 1 YOS
2/1/02 to 2/1/03 - Anniversary date - credit 1 YOS

There is an overlap in the 2002 year because of the change in vesting calculation.

Or is it

1/1/00 to 12/31/00 - Worked 1000 hrs - credit 1 YOS
1/1/01 to 12/31/01 - Worked 1000 hrs - credit 1 YOS
1/1/02 to 12/31/02 - Worked 1000 hrs - credit 1 YOS
10/1/02 to 10/1/03 - Anniversary date - credit 1 YOS
does the effective date of the amendment now become the date you count from for elapsed time purposes?

I tried to read Treas. Reg. 1.410(a)-7(f), and DOL Reg. 2530.200b-9(f), but there were no examples, and I am having trouble interpretting.

Thanks!!!