There's no definitive answer here at the moment, but this post is here to record what I have observed over the last couple of years research.
The most telling pictures are from bikes that have been dragged from barns, unrestored. Unfortunately none of the pictures clearly show the coil mounting on early bikes, only hinting at where the coil is. This post is also worth a look, as is this one.
Here we go.
|Restored 1951 bike with coil on bracket behind battery|
|Restored 1952 bike with no evidence of bracket behind battery - I've no picture of the under seat area on this bike|
|Restored 1952 bike with coil on mudguard|
|Unrestored 1949 machine with coil on mudguard. Unknown bracket behind battery.|
|Unrestored 1951 bike with coil on bracket behind battery & hitherto unknown regulator shield & brake pedal stop|