New Safe Harbor Plan started mid-year

6 doctors each had their own tax entity and shared employees who were all on the payroll of a separate tax entity.  One of the doctors (Doctor A) maintained a 401(k) plan in 2021 and covered employees for the portion of pay allocated to her based on their time worked for her and all hours worked for all doctors were counted in meeting eligibility.   I'm told none of the other doctors funded any type of plan, no Simple,  nor SEP.

They were convinced to form a group in which they are all equal shareholders and want to have one 401(k) plan covering all doctors and all eligible employees.  It will provide only a safe harbor match.  The plan has not yet started for 2022 and so there has been no plan funded by any of the doctors yet for 2022.  The goal is to have it set up by July 1, 2022.  

The thought is the group would assume sponsorship of Dr. A's frozen plan.  I wouldn't think there'd be any issue with safe harbor treatment for 2022 being adoption by a newly formed entity.  I'm also wondering about the new plan tax credit available for each of 3 years.  Seems that would require the start up of a new plan and closure of the old.  Yet for one of the 6 doctors, the plan is not new under her tax entity.  I may just not mention the tax credit if it is questionable and leave that to their tax advisor, if he even has that on his radar.

Comments as to safe harbor treatment for 2022, the tax credit?

Thank you for your comments.