Disability Program question

Hope this is not a dumb question:

We have a client who has maintained an employer-paid disability program for over 20 years.  New executives were able to join on the renewal date each year,  provided that they had one year of service by that date.

 

Last year, to entice an executive to join their firm,  they allowed her to enter the plan without the required one-year service credit.

 

There are other new hires for the coming year.  Should they be allowed in without the required service credit or can the employer make them wait until they have 1 year of service?  In other words, can the employer make an exception for one executive and then go back and manage the eligibility like it was done prior?

 

Thank you !