(b) Such benefit charge notices shall become conclusive and binding upon the base period employer unless, within 15 days after the mailing of the notice thereof to the last known address or in the absence of mailing within 15 days after the delivery of such notice, a base period employer who is subject to assessments under § 3345(a) of this title files an application for review seeking relief from benefit wages or benefit charges charged to its experience merit rating account. A § 3345(a) of this title base period employer who has filed a timely application for review of its benefit charge notice shall be entitled to relief from such benefit wage charge or benefit charges charge contained in such notice only on the basis that: (1) the claimant's separation from the base period employer (if such separation was separate from and prior to the claimant's separation from the claimant's last employer and if the base period employer is not also the last employer) was not qualifying under subdivisions (1), (2) and (7) of § 3314 of this title and(2) The Department administratively erred in calculating the correct amount of certain benefit wages or benefit charges charged to its account. However, as to paragraphs (b)(1) and (2) of this section above, any such base period or last employer who has failed to return a completed separation notice which is applicable to the benefit wage charge or benefit charges at issue in a timely manner in accordance with § 3317 of this title shall be barred from seeking benefit wage or benefit charges charge relief unless the Department for reasons found to constitute good cause should release the base period or last employer from the default. Regardless, no employer shall have standing to seek benefit wage or benefit charges charge relief pursuant to the procedure established in §§ 3317 through 3325 of this title.