Multiple lookup fields out of same table

OK, I am going to provide the details and then I will also provide some examples.

We have cruise certificates that certain partners (aka Vendors) purchase from us to use as incentives and/or gifting.  There are 2 distinct types of certificates:  one covers a portion of the cost of the cruise (incentive) and the other one covers the entire cost of the cruise (gifting).  Certificates are coded by a Vendor Code, a Location Code, Certificate # and  Issue Date.  Each certificate has a life of 18 months - it expires 18 months from the Issue Date.   The recipient of the certificate must redeem that certificate with my company.

All of the certificate information is loaded into a table "Cert Tracker".  So, in my table "Customers", I have a lookup field to pull the certificate into the customer record.  Up until recently, this has worked great.  Now we are having instances where a customer is issued more than one certificate, or 2 certificates but from 2 different vendors, but all falling within the same general time period.

For example, Susie renews her membership early with her vacation club and as an incentive to do that, she was given a cruise certificate and then 2 months later, she qualified for a cruise certificate with a completely separate vendor by selling so much of a product.  She now has 2 certificates that have to be used within 18 months.  Because of this, I was attempting to do the many to many with the middle table, but I am not seeing a way to convert the existing issued certificates over "painlessly".

One reason it is important for me to be able to link the certificate to the customer record is because I do pull data regarding overall usage, vendor specific usage, customers using certificate but upgrading, etc.  When that customer calls in to book their cruise, we normally provide multiple quotes and I would like to be able to link or reference which quote is done based off of which certificate and then as the quote then becomes a booking, it can show that certificate as redeemed.

I do tend to overthink things, so perhaps there is something I am missing or making harder than it truly is.  I apologize in advance for that!

I am attaching a couple of screenshots, but please let me know what more you need.

Thank you for your patience and assistance!

Kim