Extended Memory module and HP-41CX

[grsbanks]

Quick question...

Looking at the leaflet that comes with the HP-82181A Extended Memory module, it says:

Quote:The HP 82181A Extended Memory Module provides an additional 238 registers (1,666 bytes) for use with the HP-41C or the HP-41CV.

Obviously you need the HP 82180A Extended Functions Module to be able to use it, so why can this not be used with the HP-41CX, which has the X-Func module built in? Or is it maybe a case of this particular module being produced before the 41CX was released, hence not mentioning it?