Update old block attribute tag without losing values?

I've inherited a pile of 20 year old drawings. The BOM data was entered in blocks that have "X" for all of the attribute tags. I created a new block with the same name (ITEM) with the proper tags and am able to extract it beautifully with a template.txt file. However, if I update all of the existing ITEM blocks with the new ITEM block, the data values disappear. I can rename the "X" tags to their proper names (such as QTY, Description, etc) in the properties window, but the block tags don't update. Without unique tag names, I obviously cannot extract the BOM data. I willing to try anything at this point, does anyone have a lisp or anything? Help! Thanks! (BTW, I have 2018 pro running on win 10)