The Art World does a lot of work to generate artificial scarcity. I might have the artist wrong here, but let Dan Flavin at any rate stand in for whatever sculptor in fluorescent light tubes I am thinking of, if he isn't the right one.
Many of Flavin's works would be easy to reproduce, they're simply an arrangement of commercially available fluorescent light tubes. Many of his works exist only as descriptions of that arrangement, because many were never even assembled during his lifespan. At least for a time, much of his work existed only in potentia, being perhaps the third in an edition of three, which had not yet sold (and therefore not yet built).
The thing is, if you own a Flavin but don't have a certificate, you don't own a Flavin, You own a lamp.
Somewhat controversially, the estate is now banging out these things, with certificates, natch.