Michael Heerdegen <michael_heerdegen@web.de> writes:

[...]

> | Debugger entered--Lisp error: (void-variable displayed-month)

Ok.  So AFAIU, one (overlooked) difference between backward/forward
commands and scroll commands is that the latter are taking care of an
event parameter that is used to execute the command in the context of
the calendar buffer.

So after all, I think we should be using this "scroll framework" to
scroll years also.  Here is an updated patch that could be applied on
top of master.