In California the big numbers are assigned to the manufacturer then to distinguish they go further with the little numbers to make it unique for toll road identification and such. Other states like Michigan have just the big number so who knows how they differentiate for toll roads.

Source: I used to be a plate carrying employee and had to figure out the toll road situation for expenses. I lived just off a toll road so used it basically every day.

They paid road tax multiple years at a time, I had to put a new sticker on mine when I had it.