Beware of walk on fares being cheaper than fares booked for nominated dates on line

If I understand him correctly, fares supremo Barry Doe is saying (in Rail Magazine issue 770) that on some ticket websites (he does not name them) if you tell the system the date you are returning it doesn't offer you so-called open returns that are cheaper.

His example  is booking a journey where the out leg is a bargain basement £20 and the return leg is £73. Buyer assumes that £93 total is a good deal, but because s/he has not selected "open", the cheaper, walk-on return fare of £74 is not offered.

None of this is helped by the confusing and fairly recently changed nomenclature for the different tickets, especially as terms like "open" have changed their meaning - it is not an entirely new set of terms replacing the old ones.