There's no reason why RE & WR would not be identified as a 'married' couple, either before or after the date of assignment. There must be some doubt, however, that they were legally married.

It's very unlikely that a convict would be assigned to another convict but assignment to an ex-convict was quite common. The assignment is dated Sep. 1823 & the shortest sentence then prevailing was 7 years. This implies that an ex-convict master's sentence would have had to commence no later than, say, early-mid 1816. This would appear to eliminate William 'Baring' ROBINSON as a suspected 'husband' but places either of the William 'Lord Eldon' ROBINSONs in the frame. It does not exclude other WRs, whether 'came free', 'free by servitude' prior to Sep. 1823 or 'born colony', from consideration.

There's some persuasive circumstantial evidence that one of the William 'Lord Eldon' ROBINSONs is indeed Rosanna's 'husband'.