in crystal the joins are not enforced (unless you explicitly make them so) until a field from the table is used.
Since you cannot left join with excel you may be dropping records when you use a field from any source for the first time.
It is quite odd to watch a report jump from a million records to 0 just by adding a field to it (i just did that about 5 minutes ago because my join was on the wrong field)
Edited by DBlank - 22 Dec 2009 at 12:43pm