Not sure i can help you get your joins right but maybe a little info will help you.
When you create joins in Crystal the join is not inherently enforced. Meaning it acts as if it does not exist unless you either
1. Enforce the join in the join set up (middle part in the "link options" window)
2. Or you use a field from both tables in the join.
Option 2 explains why records are disappearing from your report as you add a field from a new table.
Edited by DBlank - 08 Feb 2011 at 5:31am