Well, err .... so possibly no signature for the 1850 marriage .... so err ... as yet there's actually no confirmation opportunities linking those Scottish index sightings of Gordon BLAIR with Jane NORVAL and the Queensland Australia Gordon BLAIR with Julia DROUGHTON .....
Considering that Qld Marriage Act 1865 tightened up the recording/registration process, perhaps the reason for the 1876 Qld marriage was simply that no record could be found of the 1863 Qld one.
It is entirely possible that the Gordon BLAIR in Qld has not told fibs, and the person recording the information may have mis-heard the details he provided ORALLY, (clergy can make mistakes on parish registers, even today, and transcribers can mis-read the handwriting and add to those mistakes).
NSW state archives online index includes their holdings of passenger lists into Moreton Bay. Gordon BLAIR is not there, but there is a Jane BLAIR, 33 years per William Miles in 1855, to Moreton Bay. Again, I mention that NOT ALL passenger lists to any port in any of the colonies in the Antipodes survived, NOT ALL passenger lists included names of those travelling steerage, and NOT ALL passenger lists have been transcribed and indexed and NOT ALL birth registrations arrived at or were accurately processed by the Registrar General's Office.
JM