Normally a new element set you download do not replace the previous one for the same object but add the elements for the new date.
This allow you to have in the database the element for a periodic comet at different opposition, the program use the right element depending on the date. The same is done for the asteroids. In your case there is probably a problem with the comet identification from one of the element set and the program think it is a different object. The identifier for this comet is CK07N030. > 14h41m02.06s -14°53'19.5" Cm C/2007 N3 (Lulin) 2009-02-08 05h00m00s m: 6.9 >phase: 49 ° dist: 0.7155au rsol: 1.2882au tl:0.05au ref:1/2007-10-27 > 14h41m15.68s -14°54'15.0" Cm C/2007 N3 (Lulin) 2009-02-08 05h00m00s m: 6.9 >phase: 49 ° dist: 0.7206au rsol: 1.2910au tl:0.04au ref:2/2008-11-30 We see that one element is from October 2007 and the other from February 2009. Can you look at your directory cartes_du_ciel\MPC if you still have the COMET.DAT file from October 2007 and search the identifier for Lulin in column one. Patrick
