Earlier, the post office did not use any specific numbering system but this changed when they started using a rather simple system on their leaflets: xxxx--y where xxxx is the year and y is the issue number within that year.
The post office did not use any specific numbering system. This was earlier. This changed. This was earlier. They started using a rather simple system on their leaflets: xxxx--y where xxxx is the year. Y is the issue number within that year. This is earlier.