Missed Deferral Opportunity

I have a plan that inadvertently did not offer 401k enrollment to eligible employees (non-auto enroll).  However, there were no contributions by any HCEs or NHCEs for any of the plan years involved or any matching contributions. What would be the basis for the missed deferral opportunity?  Should it be assumed that it is 3%?

To clarify, are you saying no one - including participants who were offered 401k enrollment - made any salary deferrals or received a match for multiple years?

If there are participants who are actively deferring and being matched, does the plan have an ADP and ACP test? 

If it is a safe harbor plan, what is the safe harbor design?

What is the vesting schedule applicable to the match?

Additional information will be helpful.

Not safe harbor.  No one made any contributions. Originally a soloK where the owner rolled money into the solok but has never made any contributions.