Here are the possible reasons for the inconsistency -
1) Jane Tanner lied. She never walked past Gerry and Jes although she DID at some point in time close to the time Gerry and Jes were chatting see a man carrying a child who was later identified by SY and eliminated.
2) Jane Tanner lied. She never walked past Gerry and Jes and she never saw a man carrying a child, it's pure coincidence that a man matching her description carrying a child at the time she said she saw him was identified by SY
3) Jane Tanner lied, she never walked past Gerry and Jes and the Met are lying too when they say her sighting has been identified and eliminated
4) Jane Tanner did not lie, Gerry did not see her but Jes did - the latter is lying about not seeing her.
5) Jane Tanner did not lie, Gerry did see her but lied about not seeing her, Jes did not see her
6) Jane did not lie, but both Gerry and Jes lied about not seeing her.
7) No one lied, they all remembered events slightly differently, and the men who were engaged in conversation did not notice Jane walk by.
Have I missed anything out? Can we take a vote on which seems the most plausible explanation?