"Facts: 401k Safe Harbor with Cross Tested Profit Sharing.
Employer formed LLC effective 1/1/2021, was sole-prop for 20+ years prior to this.
First payroll date was technically 1/12/2021, with bi-weekly payroll thereafter, however, the new LLC bank account was not yet established so all employees were paid a reasonable 'Advance' on 1/12/2021 equal to estimated pay (estimated hrs * hrly rate
reduced for estimated taxes etc). All employees are hourly paid. It should be noted the 401k estimated deferrals were not remitted over to the plan at this time. The plan was to reconcile all with the 1/26/2021 pay date, in the new LLC account with the new system being implemented.
Thereafter the new LLC business account was established, new system set-up, and the first official payroll was processed for 1/26/2021 pay date. With this
payroll, the bookkeeper logged all hours year to date (i.e. including hrs for pay date 1/12) making gross wages correct for year to date (both 1/12 and 1/26). Taxes and 401k* were determined, the '1/12/2021 advance' figures reflected, and the resulting net pay to employee determined.
Herein lies the problem: only 1/26 pay date's 401k amounts were accounted for, missing were the 1/12/2021 amounts. Total
401k reported as of 1/26/2021 $956.25 -- this amount was short by the 1/12/2021 payroll's total 401k withholding $922.50.
Good news/bad news: The bookkeeper caught her mistake when she remitted the deposit over to the Plan and deposited $1,878.75 -- 1/12/2021's $922.50 plus 1/26/2021's $956.25. (This 1,878.75 matches the employee deferral elections in place and gross wages paid.)
Only problem was she
never went back into payroll and made adjusting entries to 'account' for the correct 401k amounts remitted over to the Plan. Therefore, the three participants affected received the $922.50 in their net pay (i.e. in their pocket). Because of this the W2s are correct as issued.
 Can the $922.50 be deemed an employer corrective contribution and a notice issued at this time, or, should it be considered an
'unallocated suspense' amount to be applied at a later date? My concern with the former is that it is more than the prescribed correction -- is this acceptable (can correction be more than guidance prescribes) or is it prohibited?? And if the latter, can the employer apply it towards the 2021 Safe Harbor (3% non-elective) contribution to be deposited by 10/15/2022?
 If the $922.50 can not be deemed an employer
corrective contribution at the time is was deposited, a correction is needed for the missed deferral opportunity (1/12/2021 pay date). Is it the missed known amount per participant or 50% of the average NHCE deferral rate? All employees are still employed; no Correction Notice has been distributed. It is a balance forward plan."