Are there any rules about how long a company has to make plan participants fully vested when there has been a partial plan year termination?

I've been told we fall into this category due to layoffs in 2001. Also, do we need to make everyone who left our company in 2001 whole, or just the participants who were affected by the layoff?

Only those particiapants terminated as a result of the partial termination must be fully vested.