Sorry to revive and old thread, but I have this same problem and its the one thing keeping me from purchasing Express Invoice.
What's the point of having a customer order number on the invoice if it doesn't show up in the Invoice List? I see one can now also create custom fields, which is great except they don't show up on the Invoice List either!
Older versions used to have both Customer PO and Order number fields on the invoice template and I used the Order Number field for this, as that at least shows up on the Invoice List. Then after v3.65 they decided to remove that from the invoice template, which forced me to use other software. I *need* to see a reference field on the Invoice List as its the only way to differentiate between multiple invoices for the same client... I've even mailed the support address asking for this. Either put the manual Order No back on the invoice, or make the Invoice List adaptable as to which columns to display.. I've heard nothing back from them, so I just pop in every time there's a new version to have a look....
Other than that I really like the software, but its useless without displaying what I need to see... Hopefully someone from NCH reads this and passes it on to the people who write the software....