Hi ijf and welcome to the forum.
A typically nasty little challenge you have there.
If the information on the occasional third line ALWAYS preceded by the text "NOTE:" in the same position whenever the third line exists?
Does the note information ever extend to a fourth line?
If YES to the first question and NO to the second, try this.
Make you DETAIL template sample just the two lines that always exist. Map your fields - you probably already have them in place.
Create and APPEND template with a single line sample - does not matter muuch which line you use. Give it the same trap as your detail template.
'Paint' a field to start just after the "NOTE:" position on the line and make it as wide as you need it.
Right click on that field, go to the Advnaced Properties tab. IN the first section you will see an option for 'Start field on ... preceding string on the current line...' in the box provided enter "note:" (without the quote marks of course). If the note is only ever one line that should be all you need to do. If it can be longer you may need to investigate the 'End field on...' options as well.
OK the template and check what it gives you across a whole report.
In the table you should see the 'Note' field (or whatever you called it) filled only where there is a note to report.
If that does not give you a solution let us know so we can endeavour to work out why.