safe harbor match - compensation period

We have a client who opened a new plan in August 2022.  The plan effective date is 1/1/2022.  Deferrals did not begin until Oct 1, 2022.  It is a basic safe harbor match plan allocated on a plan year basis.  The match will be calculated after the end of the year. 

My question is must the match be based on compensation only from Oct 1 through Dec 31 or the entire year?  Example: Employee has $10,000 in wages each of 4 quarters.  Oct - Dec defers $2,000.  Would this person get a $400 Match (4% just on 4th qtr wages), or a $1600 match (4% on full year wages)?

Nothing in the plan limits the compensation or match period.

Appreciate your comments.

36 minutes ago, Tom said:

Nothing in the plan limits the compensation or match period.

If that's what your document says, I would think annual compensation would control for calculating the match.

Thanks Lou.  I questioned because the effect is generally to favor HCEs - they can easily defer $20,500 in last qtr of the year and get 4% match on pay for the full year.  A NHCE could defer 20% in last qtr (5% avg for the year) and get 4% match on pay for the full year.  That would be unusual for an NHCE to defer a high% in last quarter but it is possible.

On 12/12/2022 at 2:05 PM, Tom said:

Deferrals did not begin until Oct 1, 2022. 

Why didn't they? If the plan was properly communicated and the administrative apparatus in place 1/1/2022 to accept deferrals, and safe harbor notice provided before or around 1/1 when the plan was adopted, but no one chose to defer until 10/1, OK. But if the deferral feature was not effectively implemented until 10/1/2022, so that NHCEs really had no practical way to defer before that date, I think IRS might argue plan was really not effective until 10/1. The rule that a plan can generally be adopted with a retroactive effective date,  would seem to conflict with the "plan year requirement" of Treas. reg. sec. 1.401(k)-3(e) in this case.