JM,
I'll leave that one to Wiggy to answer when she resurfaces
Your questioning is quite valid-discrete facts, circumstantial evidence and negative evidence have been combined , and assumptions made that there is a connection between "wife", "McNally" and "Mrs Ransom". I have accepted and advanced that assumption, because , in the light of the subsequent evidence from 1823-1830, it appears to be an assumption with a reasonable level of probability.
However, you are correct- it needs to be proved/disproved by examination of facts and possible explanations eg the 1819 Land and Stock Muster for Van Diemens Land ( October )states Thomas Ransom , a wife and a Government Servant are on the Stores(Victualled) with Thomas holding a 400 acres land grant at Hobart. Was this a clerical error- he had no wife ?- did he have a wife who subsequently died/moved out/ left before CCM came on the scene? When did he acquire said wife?
The 1818 Free women on General Muster Hobart Town 1818 lists 328 free women ( not including Catharine McNallY), of which 206 were married. To become Mrs Ransom by October 1819 , we are left with 122 who were unmarried in 1818, plus any married women ln 1818 who were widowed during 1819, plus any blow ins to Hobart during 1819.
Some of the 122 can be elimnated by reference to the 1822 Muster- if they are still in the 1822 muster , then they couldn't have become Mrs Ransom in 1819- so we look only for those who are in the 1818 list but not the 1822 list (so excluding people such as Lucy Margaret Davey who was in the 1818 list and also the 1822 list and was the Lieut Govenors daughter). There were 45 women listed in 1818, but not in 1822- they must have died, married,moved away, or did not turn up.
Need to stop now, but would be interested in your response
David