The data source is an Excel sheet and some cells contains between 200 and 500
characters, some of it formatted with carriage returns. When the data
arrives in the Word document with those fields cut off. It seems very
inconsistent as to what fields get cut off and at what character count.

As a test I inserted text totalling 400 characters in 4 different cells that
all the merged into the same Word document. All the cells are formatted as
General. While proceeding through the Merge Wizard, I checked the fields in
question in the Edit Recipient list and it appeared that the first field
contained 254 of the 400 characters and the other 3 fields contained 255 of
the 400 characters. I backed out and double checked the contents and format
of the columns in the spreadsheet and even re-copied the cells to be sure. I
reran the merge and found the same result in the Edit Recipient list so
proceeded with the merge and the result baffled me. The first field contains
all 400 characters but the other 3 each contain only the 255 first
characters.

I am fairly new to mail merge and would appreciate any assistance helping
resolving this.