I wonder, despite what some records seem to say, that rather than there being two criminal Robert Masons in Maidstone at the same time, the seeming double record comes about because Henry Tanner was not originally the vessel he was due to go on. There was only one Robert Mason convicted at the Lent Assizes in Kent on 11 March 1833 for uttering a forged bill of exchange for £30. The date and offence are consistently the same in records of Robert Mason in 1833 and 1834. The Prison hulk registers and the convict ship sailings tell the following story:
He was initially sent, from Maidstone jail to the hulk “Retribution” at Sheerness (this hulk was at Woolwich and Sheerness at various times hence the newspaper report) which records him being received from Maidstone jail on 25 March 1833. The disposed of column, written before it happened, says that he is due to go to NSW 23 May 1833.
He then appears on the list of convicts on the Lord Lynedoch sailing 30 May 1833 for NSW.
The register for the hulk “Retribution” at Woolwich then notes him being received from “Lord Lynedoch” Bay Ship 31 May 1933. Disposed of says “Fortitude” 31 Mar 1834.
The hulk “Fortitude”at Chatham says received from “Retribution” 1 Apr 1834 and disposed of NSW 27 Jun 1834
He is then on the list of convicts on Henry Tanner sailing 27 Jun 1834 This is the record that says "Kent gaol delivery" but perhaps should have said "from Retribution".
It may be that the master of the Lord Lynedoch didn't want him aboard for some reason or another and before leaving UK waters, sent him back to the prison hulk system. See my next post.
Doesn't answer your query but thought it might be of interest.