At the risk of sounding a bit like one of your former Presidents, it depends on the meaning of the word 'lie'. Clearly, having the Wise Men (of whatever number) together with the shepherds is historically inaccurate. But does that matter in this context? It really depends what truth we are trying to convey as more important - whether the fact that Jesus was worshipped by both shepherds and Magi is more important than the timeline of that worship. Let me give a similar example, from outside of the Baptist tradition: in Eastern Orthodox icons of the Pentecost scene, Paul and James (the brother of the Lord) are depicted as being present in the room. Now, we know from the Scriptures that Paul and James weren't actually there historically; but the main point of the icon is not to show who was there and when, but that all the Apostles received and were commissioned by the Holy Spirit, including (later) James and Paul. This particular icon, just like the Nativity scene, is not meant to be a snap-shot of one moment in time, but rather a visual representation of a dynamic story, rather like a comic strip consisting of just one frame.