Need to combine duplicate member records with unique property id numbers

I have a spreadsheet containing about 97,000 names of customers. It is highly possible (and it does exist) where the customer/member has more than one Property ID (unique number never duplicated).

I want to take this excel spreadsheet and merge it with MS Word to make mailing labels, but want a cost-effective means to save on postage of sending the same postcard (with a different Property ID number) to the same address. Is there a way that I could identify which customer-members are repeated in the spreadsheet, and if necessary create a new column which would contain the duplicate's unique Property ID number? That way I could easily do a mail-merge in Word where one field could be the original Property ID number and the second field could be Property ID2, Property ID3 etc and if there was no information, Word mail merge would automatically ignore that field. I'm totally open to suggestions and tried to attach the file but it's too large 13.2MB, so if you can inbox me, I will email it to you. Thanks for the help, I truly appreciate it.

There are going to be lots of different ways to do this. I would recommend sorting the list by name, then flag rows that include repeat names. You could use an if statement like =if(B3=B2,"Duplicate","").

However, there are ways you could automate the process further, which would help given that you have so much data. If you could post even a portion of the spreadsheet, we would have an idea for the formatting of the data. Perhaps delete most of the data and post the skeleton spreadsheet?

Is there a way you can email me so I can attach the file? This way I understand the process the entire step of the way. Again, I'm truly thankful.