What does the Minox registry tell us? 

Survival of individual Serial number ranges

As you can see, the survival of all Riga cameras is very similar, until of course it hits 15250. We know that from then on cameras are found in a partially assembled state, indicating the end of official production. It is interesting that sowjet and german occupation cameras have survived at a similar rate to early cameras. You would imagine that the earlier cameras and exported cameras would have survived in greater numbers but apparently not.