New Employer

Would appreciate any opinions on a new employer using a plan effective date prior to the start date of the company.  I know the EOB says it may be possible but recommends requesting a determination letter which is not likely possible for a pre-approved plan.

Say the employer (in this case a one-man company) start date is November 1, 2019, and the employer wants to start a calendar plan for 2019.  If we make the plan effective for November 1, 2019, but define the limitation year as the calendar year, are we still good with not having to prorate limits?

Thanks.

Is this a sole proprietor or a corporation? 

What defines "start date"?  In other words, did he leave a prior job and start a new company on 11/1, or was he always doing his thing and just incorporated on 11/1?

Waiting on clarification from the potential client's CPA, just trying to cover the bases.  

In this case I'm assuming the former as the worst case scenario.

Thanks.