Wait a minute… For some reason I thought you were talking about photographic copies for print making. Not replication paintings.
When the original painter replicates their own work, by making a duplicate painting, each replication is still considered to be an original artwork. One is not any more or less valuable than the other. But when that work is replicated by another artist, or duplicated photographically, those are typically less valuable to the collector.
Often times a gallery will have sold a painting, but another buyer wants one. It should be no problem for anyone if the original painter is consigned to replicate his own work… often in a different size to accommodate the wishes of the new buyer. It’s still an original.