Yes I think this is basically correct.From memory, which can be quite dodgy these days, everyone got a maximum of 1,500 points if you had held a season ticket for 5 years or more at Maine Rd.
Check on your City account and it will show it. If not best contacting the ticket office.
When points were first introduced, everyone got allocated points based on how long they had been a season ticket holder up to being a 'regular' season ticket holder, which was 5 or 6 consecutive years.