Many years ago I fitted double the "maximum" amount of RAM specified by the manufacturer. The maximum capacity mentioned in the laptop user guide differed from the Kingston web site. The figure on the Kingston site turned out to be fully compatible.
I suspect that when the laptop manual was written, the largest SODIMMs available were 2GB. By the time 4GB memory became affordable, production of the laptop had ceased, so there was no incentive to update the manual for an obsolete product.
If your system isn't used for critical work and new RAM isn't too expensive, give it a go.