Again, think about addresses (e.g. 11A; technically is a number - do we have to use pa'ypa'y just because of the A at the end of it?), registration numbers, etc.
We can rework systems like my date system or Pierre's coordinate system to fit whatever Lojban evolves to, since they are meant for Lojbanic use. But we can't rework every irregular numeric system in everyday life.