Sounds like we would need a sample presentation to to really see what is going on but what I have done for something like this is choose 1 slide for data usually the last slide. Make this slide hidden from the rest of the show and then keep referencing back to the data that I need. For example If I was looking for a way to keep a running total I would have a shape on the data slide called total. I would then set the reference using.
Code:
Dim TotalValueShape as Shape, LastSlide as Integer, TotalScore as integer
LastSlide = activepresentation.slides.count
Set TotalValueShape = activepresentation.slides(LastSlide).shapes("Total")
TotalScore = TotalValueShape.textframe.textrange.characters
Now with this reference you can set the TotalValueShape.TextFrame.TextRange.Characters to whatever value you get from your calcualtion and then keep referencing back to it.
Sorry if this is confusing there may be a better way but its the way that worked for me.