From what I've seen, 808nm diodes are about 35-40 percent efficient, i.e. at 2.2 volts and 1 amp that should be close to 900mw, maybe the efficiency can be higher for some.
Perhaps the range of voltage and current are as wide as they are because he is selling slightly different diodes, or they vary by that much from unit to unit. I have to admit, those are some very wide differences and that would explain why you see some diodes which are specified within those voltage and current ranges to have much different output levels.
I don't know why the seller has specified such wide possible voltage and current ranges, ask him, it isn't common for a 808nm diode to require 2.7 volts but like I said, he might have mixed devices or lots which behave differently (or didn't know what they were doing when testing them and didn't account for the voltage drop from the power leads, or... knows others don't). Still, I'd expect he isn't misrepresenting anything and that those are indeed the differences which can happen from diode to diode that he sells. However, the lower voltage and current numbers he stated are completely normal for a 40% efficient 808nm diode.
