How does the initial eligibility computation period work with someone who is something of a transient worker? Say he or she first ever performed work for an employer in 1989, leaves eight months later in 1990, returns off and on again over the years. Does this mean that his or her initial eligibility computation period still remains the year from when he or she first ever worked for the employer?

what is the plan's definition of 'break in svc'? did the ee meet the eligibility requirements previously?
for example: plan imposes no break in service
ee worked 1000 hours but failed to meet entry date requirement
ee quits and later returns to work a year later
this ee enters upon date of rehire because they satisfied the eligibility requirements and they have now passed (or if you will) reached the next possible entry date.