Forms :: List Box Should Be Filtered As Readable Characters Entered In Text Box

I have a table with a huge master list (some hundred thousand) of unique bar code tags, which either have 8 or 12 digits. (Valid characters are "012 345 678 9ACEFHJKLMNPRYXW"). I created a form, which is automatically looking up valid records as the string is entered position by position from left to right. This is working fine and sufficient in 99% of the cases.

Sometimes characters are not readable on the original document, so I need a tool/form, were I can enter only the readable positions of the code and the tag list is then filtered accordingly. For that, I created a separate form with 12 text boxes for each possible position of the bar code and a listbox. This list box should be filtered as the readable characters are entered in their respective positions/textbox.