I don't think that when witnesses remember additional details and add to them to a previously given statement it constitutes a 'discrepency' ( and that includes Jane Tanner's statement )
People being asked, on re-interview, if there is anything else they can remember about an incident seems perfectly in order to me ... and if they do remember additional details, then that is a good thing. The original statement remains unchanged with more details added
What constitutes a discrepency is not additional information, but altered information
Gerry McCann saying he went into the apartment that night through the front door using a key, and then altering that statement to say he went in through the open patio doors is not additional information, it is altered information. The original statement has been 'changed, rather than added to ( a discrepency )
Similarly, when Kate McCann said the curtains were open when she went into the room at 10pm and then said later that she had found the curtains to be closed, she did not add details to her statement, she changed it ( a discrepency )
Where a new witness statement adds to, but does not conflict, with a previously given statement, there is no discrepency