Can anyone explain why closing bid prices & mid vary so much against each other depending on where you look!

e.g. GSK Friday - streaming bid price closed @ 12.37

With after market closing dealing the MID(?) price ended up @ 12.05 and this also was the mid (?) price quoted in the newspapers over the weekend. This also seem to be the opening mid(?) price everywhere this morning.

So what is the real closing bid price? The closing mid(?) price or closing bid price?

It used to be so much easier..............