Merge two cells, no duplicates

Hi, I'm a first-time poster and have an issue that is really baffling.
Unfortunately, I am working on an xls which is data from a database that is being moved into a new database.

The columns don't match between databases and the datasets also need converting. For background, I work for an asbestos consultancy.
I'm using XLOOKUP to match the original data with the required new data.
Where I am now having an issue is I have two rows, Asbestos Type 1 (AO) and Asbestos type 2(AP). These are being merged into a column with comma separation (AQ) which is then used to do a lookup in column (AR) .

I can't have duplicates in the new data so I am using the following formula.

The formula used is in the attachment in column C "Asbestos Raw" as it's getting seen as a link here

The issue is when I have a blank second cell which is the case for a lot of the data I get a #NA as there is no data.
Any clue how to correct the above formula or a better way to do this?

Thanks in advance to anyone who can assist.

Hi Ali, Thanks for your reply. I've changed the sheet and made a mockup of what I need. You can see where I started by using TEXTJOIN which keeps the duplicates.
So the trouble column for me now is just column C.
I had tried TEXTJOIN using MATCH to look for the duplicates which did work, but because sometimes column B is empty it returns the error #N/A

Thank you