This limitation is a pain in the neck. AFAIK there is no way to access a
count of the number of formats.

One issue is that a cell  format is any different attribute of a cell. for
example if you have a cell with a thin bottom border, that is a different
format to a cell with a thick bottom border. Each colour (background and
foreground) can be different, fonts have a number of attributes, etc. So the
number of possible formats  (combinations of all the attributes) is enormous.

If you start with a blank sheet, then

Select some cells and make them bold (you have two formats)
Select some cells including some but not all of the bold ones and make them
red (you have four formats)
Select some of the cells and set a bottom border (you now have up to 16
formats) - remember some cells may have top borders now, some bottom, some
none, and some both and each of these can have bold or non bold fonts and they
may be read or default .

This is made even more difficult because excel is very reluctant to lose
cellformats, even if they are not in use.

If you now select an "unformatted" cell and copy it
Select all cells
Paste Special - formats
All the cells are now unformatted

But: You have still used 16 formats!

To work around this you might think you could simply import the workbooks, one
at a time and then select the newly imported workbook  and delete all the
formatting or remove the formatting from each workbook before importing.

It will not work.

You may need to import the values only from each workbook. For example by
using copy and PasteSpecial values.
You might also PasteSpecial formats if you need the formats. This should only
paste in the formats which are really in use (I think).

I hope some of this may help. Please let us know how you get on.