Can values from UDF on multiple tabs be displayed on another tab? (Excel 2003)

I have a huge quantity of data coming from a client.
That means I have no control over the format.
There are 2 tabs for each day of the week that I am trying to summarize the data on another tab.
The data requires summing, averaging, min and max calculations. Additionally, the analysis has to ignore cells with no data and bad data (generally "--") which means that I needed to create UDF functions for MIN, MAX. I also had to create one that reads a range and once it locates the maximum in that range, it returns the value from an adjacent cell, using an offset value. I call it MaxAtOffset(rng As Range, offst As Integer)
On each tab, I can get numbers to generate and can summarize each tabs values.
But when I try to bring these values together onto another tab to create my overall summary, the values do not show. Occasionally, some display but when I move off of the tab and come back, they all revert to zero.
I tried making the UDF's in an add-in but that did not help. I added application.volatile to my UDF's but that also did not help.
I have all recalculate check boxes checked in the options dialog box that I know of. And used Ctrl+Alt+F9.