changing source file doesn't save

I am having a problem in powerpoint. I have a 60 page presentation I send
out on a monthly basis and it's mainly linked to excel files which we update
with monthly essbase data.

For example, I copy the May files into a June folder, rename them June and
start updating the excel files with June data and headings. I then update
the links in powerpoint to point to the June files, save and send out. Now
sometimes there are changes that come in and I may need to update the excel
files and update the links in powerpoint.

The problem I'm having is when I try to do this... although the data on the
presentation is the original updated june data, the link is pointing to May.
This can be a problem if I have to do a sweeping change that effects all 60
pages... I can't just hit update links... I have to manually relink all 60
pages to june file.

Thanks for the help!

-Arthur