The correct lamp assembly for the 9N is the N90 - the same as for the 9AN, the B92 rechargeable battery was discontinued and replaced by the B90. So the B90 will be the right one for you.
Yup same lamp, BUT the older lamp assemblies, when the hi output bulb wsa activated, the low-output lamp was not. On the new lamps, both lamps light-up when the hi output lamp is activated.