HELOC Initial Disclosures and 15 yr Table

I'm normally accustomed to reviewing the 15 year historical table in HELOC disclosures given at application and seeing Margin added to Index value to equal an APR for each of the 15 years. The only reason, in my opinion, the APR wouldn't be the total of Index plus Margin was if a floor or ceiling rate came into play. Unfortunately, I'm viewing a number of HELOC account opening disclosures where the APR doesn't seem to equal index plus margin and where a floor or ceiling should have had no impact. Any thoughts of a situation where the APR could deviate without the impact of a floor or celiing rate issue????

Thanks.

Is there an introductory rate involved with these transactions?