virtual at Reserved.BASE
Reserved::
;       db -1 ; no longer an error, 17 byte contents retrieved.
        rb 16
end virtual

Reserved.BASE:
        contents AreaContent Reserved ; error when no initialized data    

My present work-around is to examine $%%

FIX_BUG         := 0
USE_CALM        := 0

virtual at Reserved.BASE
Reserved::
        if FIX_BUG
                db -1
        end if
end virtual

Reserved.BASE:
virtual Reserved
        rb 16 ; bug only happens when the whole area is uninitialized
end virtual

if USE_CALM
        contents AreaContent Reserved
else
        load contents:sizeof Reserved from Reserved:Reserved.BASE
end if

db contents

calminstruction(target) AreaContent? area*
        local string
        load string, area: 0, sizeof area
        publish target, string
end calminstruction    

virtual at _Data.BASE
_Data::
        db 0
        db ?
        db 1
        db ?
end virtual

_Data.BASE:
load contents:1 from _Data:_Data.BASE + 0
db contents
load contents:1 from _Data:_Data.BASE + 1
db contents
load contents:1 from _Data:_Data.BASE + 2
db contents
load contents:1 from _Data:_Data.BASE + 3
db contents    

; add a defined byte to force trailing undefined data to zeroes
calminstruction(target) AreaContent? area*
        local string, line
        arrange line, =virtual area
        assemble line
        arrange line, =db -1
        assemble line
        arrange line, =end =virtual
        assemble line
        load string, area: 0, sizeof area - 1
        publish target, string
end calminstruction    

struc (contents) AreaContent area*
        virtual area
                if $@ = $
                        load contents.db:$-$$ from area:$$
                        contents.rb = 0
                else
                        load contents.db:$@-$$ from area:$$
                        contents.rb = $-$@
                end if
        end virtual
end struc