I would be looking at a lot more than that to determine the differences.

If it was up in KG's then it was probably rated as a better chance in its last start relatice to the competition it faced in the second last start by the handicapper.

Other questions :
How many horses were in each race ?
What was the competition factor (how hard was it to win each race) in each race ?
What did the horse do at both races .. did it have a bad jump ?, was it caught it up in the straight before it could get away, did it go too hard early ?
Did the horse race with an apprentice at either race ?
etc,
etc,
etc.

Thats jsut a start but I think this should give you an idea of what should be looked at.

Its a long hard toil if you want to handicap properly ... but can be worth it.

Good Luck....