Hey, I do have other candidates for the parish baptism record for Janet Sinclair and still quite a few to look at. The baptism records for her and James Mackay's early children mostly say that they were living in the town of Thurso and the ones which do not, do not give a location. I have often found that couples moved to the woman's place of residence to have children in these times, so she may have been from the town.
The problem I've got is that I am pretty much certain about the dates for her husband James Mackay. I am pretty certain that after their last child was born in 1778 that he joined the British Army in the same year and served in the 76th Foot under the Earl of Caithness, before moving to other regiments. He discharged twice from the army, first in 1802 aged "about" 48, and secondly in 1814 aged "about 60". The two records both match up with ages and suggest that he was born in about 1754, which in turn means that he would have only been about 14 when his first child was born in 1768. I know this is less of a problem with men, but it is still a bit on the young side.
The other problem is that I am pretty sure I have the same James Mackay on rent records in the village of Armadale, with his "widow" being recorded in place of him from 1833 onwards. This would mean that he lived to about 79, which is fine, but his "widow" appears in the rent records until 1849. I know women generally live longer than men but this is stretching it a bit, especially in those days.
Although the 1768 OPR for their first child does not give their location in the parish of Thurso, it does give the witnesses as William Mackay of Kinloch, who I know died in Thurso in 1772, and Patrick Doul of Oldfield which is very close to the town of Thurso. The 1770 OPR for their second child does say that they were then living in the "town" of Thurso and the witnesses are William Sinclair and Helen Sinclair. I am just wondering if this William Sinclair was Janet's father as there is an OPR for a Janet Sinclair dated 1743, daughter of William Sinclair, also "in town". This would make her 25 when her first child was born in 1768 and 35 when her last child was born in 1778 which fits nicely, but does not account for the young age of her husband James Mackay as per the military records.
It also does not account for the rent records in the village of Armadale where I believe they lived at a later date, but I am now thinking that this could have been one of the sons named James born to James Mackay and Janet Sinclair.