This is confusing. Enter the code where? Come back to where? When you enter sales invoices, you are in an entirely different functional tab than when viewing the list of non-inventory items. So it is impossible to understand what you mean by this. Please explain.
I already stated in post #8 that your comments about codes when entering invoices are not clear. This additional comment just adds more uncertainty. What shows in numerical ascending order when you open a sales invoice? As I mentioned previously, the only thing on the entry screen for sales invoices that could be in ascending order (or not) is the dropdown menu for Item selection. And I already addressed that.
If you are instead referring to opening the Sales Invoices tab and seeing the list of sales invoices in ascending order, then you simply have not seen enough data to understand that display. Sales invoices in their tab listing are not sorted in ascending order. They are sorted according to a multi-part algorithm in which the first criterion is status, then issue date. See Sales Invoice sort order - #3 by Tut, as well as the rest of that thread.
I also call your attention to the fact that sales invoices have no codes. They have reference numbers. that is an important difference in Manager. Terminology is important when trying to understand perceived problems.