Excel 2007

I created a regular .xlsm workbook with a user-created function that
calculates the date of the deadline x days from an entered date. The
result depends on whether a weekend intervenes, whether the deadline
would be a holiday (in which case the next day becomes a deadline),
etc. The list of holiday dates, which has to be updated every year,
is found in a named range on a separate sheet in the workbook. The
main function calls a macro, which in turn works out the final
deadline based in part on whether the tentative deadline appears in
the range of holiday dates.

This function turns out to be useful in other worksheets. So I
thought I would store it and the holiday list in an add-in (.xlam) and
keep the orginal .xlsm workbook only for the initial data entry sheet
(date and x number of days gives deadline).

Unfortunately, I can't make this work. I have the add-in loaded and
the references set up properly. I **think** the problem is that the
macro cannot obtain data from the list of holiday dates, now in the
add-in file. Is that worksheet hidden, or simply nonexistent? If
it's hidden, can named ranges on the worksheet be referred to in the
macro stored in the add-in's code? (Another problem: With the holiday
list worksheet invisible and totally inaccessible, apparently, I can't
adjust it year to year.)

What would be a solution? Put the list of holiday dates and central
macro in personal.xlsm? Thanks for any help.