Not much thought really, to be honest....
It seems not even the Italians have found enough material to explain how this early E-M-S standard they adopted in 1912 actually worked
Even Gregory Alegi tries to avoid the topic as much as possible in his WD 108.
Most Blériot XI seems to have carried a M prefix for some reason.
Oddly enough we thus have E, M and S prefixed aircraft. Co-incidence?
No idea.
Since that initial system ment aircraft of different types could have the same number and even prefix
(Alegi specifically quotes M35 as such), someone realized they needed to get a combined system, and such a system was
in place I believe when WW 1 broke out in Europe.
I have knowledge of one re-serialled aircraft....not much to decorate a X-mas tree with...
Cheers
Stig