As it was a retention incentive, a minimum qualifying period of 5 years was stipulated. If you left before the 5 year period had elapsed you got the standard pension for your rank.
My understanding is that
was the case when PAS was introduced, but the 5 years min was changed (read withdrawn) shortly afterwards when it was legally challenged. Confusion then prevailed for a number of years as people got PAS & 05 pension 'rules' mixed up.