CGC, CBCS, and PGX graded collectibles, how do you handle slab certification IDs?

Graded collectibles are slabbed by one of three certification companies:

• CGC (Certified Guaranty Company), the dominant grader, owned by Collectors Universe. Each slab has a unique certification number printed on the label (e.g. 4012345678). Buyers verify the grade on cgccomics.com by entering the cert ID.
• CBCS (Comic Book Certification Service), the #2 grader, acquired by Beckett. Cert IDs follow a similar format. Verified on cbcscomics.com.
• PGX (Professional Grading eXperts), smaller third grader, controversial in the hobby due to historical grading inconsistencies. Cert IDs verifiable on pgxcomics.com.

The Magento implementation: each graded slab is a unique Magento product (not a configurable). Custom attributes: grader (CGC/CBCS/PGX), grade (e.g. 9.8), cert ID (unique, indexable), signature series (yes/no), pedigree (yes/no, with collection name), restoration disclosure. PDP renders a “Verify on cgccomics.com” deep-link that opens the cert-lookup page pre-filled with the cert ID.

SEO win: each cert ID generates a unique canonical URL, indexable by Google. Collectors search for specific cert IDs, ranking on those queries captures buyers actively hunting for the slab.