Big word for one of a kind

I’m looking for a specific adjective for a product (meaning something created by a human and not naturally occurring) where there is only one unit ever produced.

Similar meaning to bespoke but that implies it was created for a specific purpose. The word I’m thinking of can be used for items that don’t serve a specific purpose; eg: an art piece.

By definition ‘unique’ fits, but in common usage it generally means unusual, and not specifically one-of-a-kind.

Sample sentence:

Company XYZ acquires, restores and trades a variety of rarefied collectibles, from classic vehicles and timepieces to artworks and _______ artefacts.

Example: Handwoven carpets where they couldn’t make another one exactly like it even if they tried. Or if Bugatti created a custom one-off car for a monarch.

For clarity: The word in question is not one-of-a-kind, one-off, bespoke, unique or one-of-one.

Note: This may be a loan word borrowed from another language, but generally accepted in English usage.

-EDIT-

With reference to comments below:

Agreed that this is not strictly a matter of language; rather, it is a matter of usage. So yes, any answer would be a matter of opinion. However, I don’t believe that equates to invalidating this query. Unique is academically correct, but considering this will be used in marketing material for the mass public, it’s important to consider the commonly understood meaning and connotation. For instance, using ‘one-of-a-kind’ leaves less room for ambiguity than ‘unique’.