Yep.
Some services have invoice numbers that are not tracking numbers.
Small and Light Packet are two of those.
If you printed the label from PP, the invoice/tracking number is also on the lower half of the label. Personally I cut those off and staple them to my copy of the buyer's invoice, after handwriting the shipping date and the postage cost on it.
If you hand your parcels to the counter clerk and ask, she will give you a print out that has the invoice /tracking numbers on it. If you don't ask, she won't bother, since the barcode is already on the package.
When I use a PP shipping label, I give the number to my customer along with the date of shipping and the service I used. It's no secret and I believe it gives customers more confidence.
