The mysterious Royal Enfield "Street Triple"

In 1915, during World War I, Royal Enfield produced a 675cc two stroke tri-cylindrical motorcycle. I affectionately call it the "Street Triple" since it has the same displacement as Triumph's 2007 bike of the year. Being a factory prototype, it apparently was never shown to the public. It was not put into production and Enfield carried on with singles, slanted singles, twins and later parallel twins through the rest of its existence. The National Motorcycle Museum in Solihull speculates that the 35mpg fuel economy was the reason it wasn't marketed. The engine was essentially three single-cylinder two-strokes put together. The triple engine was forgotten and the bike was lost. However, in true Enfield form, the story gets richer! Fast forward to 1967...

It turns out Royal Enfield operated a museum in its Redditch factory, apparently perhaps the first "factory museum" in motorcycling history. With the factory's demise in 1967, bits and pieces of the museum found their way to the press. In particular this photograph of the Street Triple, What astonished the journalist that published it was that the license plate ABP4 was registered... in 1934! That is, apparently the triple survived and was actually roaming the streets in the 1930's. The journalist did not know what happened to the machine, but we now know. Apparently Enfield kept the prototype in its museum (an article reports it being there in 1930) but then apparently handed it over to an enthusiast that restored it in the 1930's and made the rounds in club events, etc. It is now in the National Motorcycle Museum in Solihull. Here is another picture of the beautiful triple engine (look at those three decompressors!), According to the journalist who saw it in the museum in 1930, the triple had the habit of starting in reverse, something the rider only discovered when the clutch was released!

Don't have enough of this stuff? How about the FOUR cylinder prototype from 1919, also baffling moto-journalists, this time in 1953, I don't know where the four is. But it also apparently survived. Here is a picture I found on the internet, it looks like it is in a museum somewhere, Was Royal Enfield the only company in history to produce single cylinder, v-twin, parallel twin, triple and four cylinder motorcycles? Could there be other mystery Enfields out there that have been lost to history but are still in the hands of individuals?