It was only after executing an extended function through alpha naming (e.g. XEQ ALPHA "DDAYS") that all the extended function appeared at the end of the [CATALOG][FCN] menu; before that they were not there.
Of course it is possible that I did something that effectively switched this off, but can't figure out what...
Extended functions in menu
Extended functions in menu
34C -> 11C/15C -> 42S -> DM42/DM41X