Data merge not listing all spreadsheet entries

InDesign's Data Merge has no "deduplication" feature, and using a database I have to try and replicate the fault, I created a 30 line database and duplicated one of the rows ten times in a row, and could not replicate the fault being reported.

There's no way to really tell without looking at the txt/csv file in a text editor such as textwrangler or bbedit.

Doing so may determine:

• characters that ID doesn't recognise as legitimate characters and treats them as text (e.g. such as soft returns that have been interpreted as an unknown character)
• if any of the lines are purely blank. Data merge won't treat a blank line like a record, instead it will skip the line and take the next line as the next record. This can be demonstrated by creating a 10-line text file and adding a header row, and then in lines two and five, type any records, then import the data into data merge and it will show only two records, those of lines two and five.

What happens when you export the file as a different format from excel, such as a tab delimited file? Do the same issues persist?

What happens if you import the Excel file into a new document - are all of the rows there?

I suspect the issue lies with the database, not InDesign, but can't confirm that until these checks are carried out.