Bob,

  You haven't described the structure of the data you're downloading
per Center/day. Is it one column or many? Is it always the same set of
columns per day, and/or per center?
   Generally it would be far easier to let the mainframe store the
data and just use Excel to query the data you need when you need it. A
critical question thus becomes: what kind of database software is
running on the mainframe? While it would take a bit of VBA magic for a
front-end UserForm to specify the data you want downloaded and how you
want it summarized (in order to generate the required SQL statement)
assuming your mainframe software allows an interface to VBA, it would
be whole bunches easier over the long term to do it that way than
create and maintain large number of Excel worksheets or files to hold
the data which already exists somewhere else.This type of adhoc
query/front-end structure would also let your Master Center numbers
automatically inherit any data eidts/changes done to the mainframe data
after the initial download -- something virtually impossible to do if
you're maintaining a separate, parallel datastore in Excel files. And
if both your data and your summary needs are simple enough, you might
even look to Access (gasp!) as a front-end.
 Assuming worst case -- the only way you'll ever get data from the
mainframe is static CSV data loaded into Excel -- do you need to store
them separately after you've summarized the data into your Master
Center file? (Law of the universe: parallel databases aren't). If all
you need is summary data, or if you can re-create the mainframe
extracts on demand, you might seriously think of dumping a complex
directory/file structure in favor of cumulating each center/days'
extracts into a Master file on a daily basis, then dumping the raw
mainframe extracts.
 Which I guess is really a long way of asking for just a few more
details about what you're trying to accomplish here. I'm particularly
curious when you write "the information will vary from day to day". Is
this substance (assumed) or structure?

= Marchand =