you have on0_<%=BFcart_Index+1%> fields, those are used for passing item options, they include an item index.
using "on0" without an index is used for passing order options.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.