PSA5050 | Irregularities: Eligible items included in a settlement not covered by the PSA
From HM Revenue & Customs · PAYE Settlement Agreements
Where you identify that items have been included in a settlement which are not covered by the PSA but which would otherwise be eligible and that a compliance review is not appropriate
treat the items outside the terms of the PSA as a voluntary disclosure by the employer (this will not affect our rights to carry out a review at a later date)
obtain all the information from the employer to enable tax and NICs payable to be calculated
settle the duties underpaid including penalties and interest, under Class 6 by employer amendment
advise the employer to apply for the inclusion of the item(s) in a future PSA.