No. That character is static and stable.

Ultimately it is 1 character per year and we're currently on J, which will turn into K on 1 January. But K may not turned into L a year after that.

The reason for this is legacy where by the year didn't / doesn't always follow the calendar... Sometimes it was fiscal and other times it was another made up date that they marked as a milestone.

So the letter denotes a block of data that can refer to a years worth of data at a minimum, and so far up to 21 months of data. Theoretically it could refer to a small amount than a year though that hasn't happened yet nor do they foresee it.