The records show that Ramsay did indeed follow on from James Dewar at 6 Union Street, and retained the 'American' theme at this address. Numbers 2 and 4 do not seem to have been in use at this period, so No. 6 was indeed 'on the corner' This first type of card must come from a year or two either side of 1869.
This reverse design is presumably later than those above, but bearing the Argyle street address, still must be before 1877.