Now, Invoice Number will be the only one viewable to the customer and the store owners. On J2Store 2.6.9, the Order ID field will not be displayed in the order history / list, invoice, and the email invoice. Many store owners felt that the random number (it is actually a timestamp) does not make any sense.
Also, you can have more control over the invoice number format. You can set a prefix to the invoice number in your store profile. Example: INV-2014-00
When customer places an order, the invoice number will be INV-2014-001. Invoice ID's will start at 1 for each unique prefix
The feature, a popular request, is already implemented in the J2Store 2.6.9 and its beta is now available. Grab it at http://j2store.org/developer-releases.html