According to an article at Smithsonianmag.com, its history can only be dated back to 1988 when it was discovered it was found in an envelope marked “This is 86 years old.” Apparently the paper stock and ink match the time period at issue. But due to lost records (from Titanic)it cannot be verified it was sent from the ship. Nor is their any proof that it was actually delivered to White Star Line in New York independent of the telegram. Nor can it be ascertained who saw it if it was in fact delivered. One interesting note from the Smithsonian write-up: it failed to sell at auction on Saturday.
Source:The Mystery of a Titanic Telegram–Did the Titanic’s owners know about its collision with an iceberg?(Smithsonianmag.com,9 Nov 2015)