there is a general rule that in century or so prior to 1752 when you see Jan thru Mar you do not really know what year it is (I had the quote from some eminent historiian but lost the atribution!) ! - the Scots moved their calendar significantly before the English (the Manx were legally the last I think in Western Christendom tho possibly Iceland might claim that prize) thus those with business connections in Scotland or on Continent might well be using NS dates - I suspect your 1673 was 1672 OS in what we would have now as 1673

The 30 Feb defeats me - is there any additional context ?