I would have expected it to work Roger but just check that you are not tripping up on the Yes / No pothole
WHERE Attribute = 'Yes' ok
WHERE Attribute = 'No' OK
WHERE Attribute <> 'No' intending to get all the Yes ..... Could be Null
WHERE Attribute <> 'Yes' intending to get all the No ..... Could be Null
have been tripped up many times.
Also, if added to a BO later then they are all neither 'Yes' or 'No' but are Null until you actually set them