True, when it comes to loading gauge one can no longer even about a standard. Most countries have several different loading gauges even for the same track gauge.
In practice I am not convinced the BART is severely impacted by their "weird" gauge (whatever is meant by that, not sure what their loading gauge is, for passenger trains the distance to and height of the platforms would be most relevant).
Stadler KISS series used by Caltrain is built at least in 3 different widths.
Auckland, NZ had (not sure whether still in use) rolling stock from the UK, converted from 1435 mm to 1067 mm track gauge, the loading gauge obviously was close enough.
Finland has engines (Sr3, Dr20) and railcars (Dm12) designed for smaller central European loading gauges. They look a bit tiny compared to other stock, but they are fully usable.
In practice I am not convinced the BART is severely impacted by their "weird" gauge (whatever is meant by that, not sure what their loading gauge is, for passenger trains the distance to and height of the platforms would be most relevant).
Stadler KISS series used by Caltrain is built at least in 3 different widths.
Auckland, NZ had (not sure whether still in use) rolling stock from the UK, converted from 1435 mm to 1067 mm track gauge, the loading gauge obviously was close enough.
Finland has engines (Sr3, Dr20) and railcars (Dm12) designed for smaller central European loading gauges. They look a bit tiny compared to other stock, but they are fully usable.