This is true. And why I would have used an O-map. You can easily distinguish between the two and also overprint in purple walls/fences that are definitely not to be crossed.
See here: http://www.aire.routegadget.co.uk/rg2/#114 for a clear example. Ruined walls (ok to cross) are shown by the dashed wall symbol. Uncrossable walls are the continuous ones overprinted in purple.
It would remove all ambiguity.
(Plus it would be safer as crags would be shown more clearly and it would help the better navigators, because you can pick better lines).
Other examples:
http://www.aire.routegadget.co.uk/rg2/#134
http://www.aire.routegadget.co.uk/rg2/#133
http://www.aire.routegadget.co.uk/rg2/#118
http://www.aire.routegadget.co.uk/rg2/#113
http://www.aire.routegadget.co.uk/rg2/#99
http://www.jk.routegadget.co.uk/rg2/#64
http://www.pfo.routegadget.co.uk/rg2/#83
http://www.pfo.routegadget.co.uk/rg2/#47