There are a number of differences between Pension Credits and Vesting Service, as follows:

Pension Credits Vesting Service
Can be earned before and after January 1, 1950 Can only be earned after January 1, 1950
Can only be made for work in Covered Employment for which contributions are required to be made to the Plan Can be earned for work in Covered Employment and/or continuous non-covered employment
Benefit amount is determined based on Pension Credits Eligibility to receive benefits is based on Vesting Service, but benefit amount is not
A participant can qualify for a Regular, Early Retirement, Disability, Rule of 95 or Pro-Rata (Reciprocal) Pension based on Pension Credits A participant can qualify for a Deferred Pension based on Vesting Service