Google 表格 - 创建新值并限制删除

Question

I'm not sure if this is possible, but let me give you a scenario and what I'm trying to do. I have two Google Sheets. One has vendor product codes from multiple vendors that have to be mapped to my site's product coding system. On this sheet there can be multiple vendor codes that map on to one of my site's product codes, like below:

Vendor Name	Vendor Code	Site Code
Armadillo	5CDE378	SITE123
Barracuda	ABCDE17893N7	SITE456
Barracuda	ZXHBW18123P0	SITE123

So in this case, there are products that have unique vendor codes (5CDE378) and (ZXHBW18123P0) but correspond to the same product and thus get assigned the same site code.

The second sheet I have pulls the unique site codes from the first sheet and has additional columns to add more information - sometimes through formulas, and sometimes hard-pasted from elsewhere. It's crucial to note that this mix exists, because it means that we can't use the sort function on this particular sheet.

Say I realize that the Barracuda code of ABCDE17893N7 is actually also the same product as the other two, and need to recode it to be SITE123 rather than SITE456. In this case, I lose the unique code of SITE456 from sheet 1, and thus it's deleted from sheet 2, meaning all of the info in sheet 2 moves up a row (imagining we have thousands of rows of info and not just these 3). I don't want this to happen.

Is there any way of stipulating that when sheet 2 grabs the site code from sheet 1 it's 'frozen' so to speak, and doesn't delete when the corresponding value in sheet 1 is eliminated? So basically I'm looking for a way to 1) fetch a unique code, 2) continue getting all new unique codes, and 3) ensure that once a code has been fetched, it cannot be deleted from the second sheet even if there's a change in sheet 1.

Thanks for your help - and let me know if I can clarify anything.