Keep in mind that 1ABC 23 was first used exclusively for October plates several years ago while other schemas (e.g. 1AB 234, 12A 345, and 123 AB4) were still being issued. This was done specifically to stop the usage of 123 AB4 plates that ended in a zero, as they were being confused with old greenies that ended in an Oscar (123•ABC, e.g. 731•BZO versus 731 BZ0). They may have decided to put October registrations on pause to allow 1AAA 23 to fill out the other months. I doubt they've run out of October registrations in that range, but since they're issuing more in other months they want the registration revenue to balance out over the year.