Single participant 401(k) no document

I have been talking with a consultant that is working with an advisor who set up a "solo(k)" early last year and funded their deferrals (at that time) for the year; later that year, the business owner hired new employees and was operating on the idea that the next year (now) they would adopt a 401(k).  However, the advisor now thinks no document, associated with the "solo(k)", was prepared, thus no eligibility criteria was established.

So is the solution:
1. Treat it as though no document has been created and remedy that matter
2. Then remedy missed deferral opportunity based on step 1 (design/eligibility criteria)?   

One of my first steps would be to ask to see how the existing account is titled.  Expect the worst - could be "...IRA."  If it is "XYZ investment company, custodian for ABC 401(k)" then odds are there is a document and the advisor just doesn't know it or doesn't know where to find it.