My fault entirely, but I think you misunderstood my question. It even confused me.
If you are a member of a yacht club, you can use the code we have assigned to that yacht club to both get a discount on our product and we would also share part of the sale price with the club. Let's say the code is SYC667.
If you have purchased our product before, you qualify for a special price. We would give you another code we have assigned to your club so you get the special price, plus the additional discount and we would share part of the sale price with the club. Let's say the code is SYC6677.
This could eventually involve dozens of club, so we wanted the codes to be similar so we would know, looking at the code, the yacht club the code was for, so we could easily give them the share they were due.
Our concern was if the codes were too similar the shopping cart might confuse them.
Could I use two codes, SYC667 and SYC6677, or others that might be similar except for one additional digit or one different digit?
Hopefully I've expressed that a little more clearly 