"The Maryland Historical Magazine" is at Cornell, but it's not very illuminating.The list is from subscription books for the support of the minister of the First Presbyterian Church of Baltimore during the years 1766 to 1783.The actual listing reads
"Adair, Christie & Buchanan1766"
The "1766" according to the accompanying explanation is the date of the roster on which the names are found.The information came from rosters datedSept. 10, 1766, Sept. 1, 1770, July 19, 1773 (2 drafts) and Sept. 1, 1783.So this entry is for 1766 only.
I did not see any other entries with "&" listed - most were just "last name, first name."
There are two listings for Buchanans:
Buchanan, A[ndrew] 1766 Buchanan, William 1766, 1770, 1773, 1783
and two for Christie
Christie, R., Junr.Feb. 8, 1775 Christie, Robert1770, 1773
The original lists were arranged by pew number.
The pledge heading the 1766 roster states:
"We the Subscribers do hereby oblige ourselves to pay yearly or every year the Several Sums by us affixed to our Names respectively, for the Support of the Revd. Patrick Allison he continuing to officiate as Minister in the Presbyterian Congregation in Baltimore Town, which Sums Shall be shall be half yearly paid to the Collector appointed by the Committee of Said Congregation.Witness our hands this Tenth Day of September one thousand Severn Hundred & Sixty Six........1766"
In addition the author notes "The subscriptions evidently were voluntary and varied according to the means and liberality of the members.The largest amount promised by one person was L10 2s 6d, pledged by Mark Alexander in 1783, thought this was nearly equalled by John Smith's L8 and William Spear's L7 10s in 1766.One pew in 1783 shared by three "takers" produced L12 a year.Some pledged less than L1."
It might be that "Adair, Christie & Buchanan" similarly referred to three families taking one pew, rather than a Christie Adair and Buchanan Adair?
The original lists would probably be more illuminating.