There are a lot of old dynos around. Chances are some were designed before the German spec was in force, so those may not comply. Some early hub dynos were designed for 2.4 w, I think, and some modern ones are designed for about 1.5 w, choosing to forego the German market. The physics of generators says that at some high speed those will probably output 3 watts if no design limits are violated. Whether that speed is "realistic" or design limits are or are not violated, I don't know.

I also can't say at what road speed most bottle generators actually satisfy the 3 watt output requirement. The only products you can nail down are the ones that have been certified as meeting the German specification. But despite the fact that the spec requires 3 watts at 6 volts at a specific speed, any of these generators will put out more than 3 at higher speeds. You'd need electronic limiting to prevent it, and there's no good reason to do that, beyond the protections that modern LED lights already have built in.