Section 2.15

Atmel 8051 Microcontrollers .. nothing device specific about that

of course,it would be nice if they mentioned that some SFRs were not in all derivatives.

'plain vanilla' derivatives never had SADDR and SADEN

Now, if you had used chips from a decent manufacturer, there would have been a definite, alphabetic SFR list in the datasheet to tell you which SFRs were implemented in a specific derivative.

There is no 'limitation' in the "Accessing External Memory" paragraph, so you can derive from this document, as well as the above SADDR, that all Atmel chips can access external memory.

Erik