§ 520. Base period. A claimant's "base period" is one of the following:

1. For the purpose of subdivision one of section five hundred twenty-seven of this article, the term base period shall mean the first four of the last five completed calendar quarters ending with the week immediately preceding the filing of a valid original claim.

2. For the purpose of paragraph (a) of subdivision two of section five hundred twenty-seven of this article, the term base period shall mean the last four completed calendar quarters ending with the week immediately preceding the filing of a valid original claim.