Your math is right, as our GAs do not seem to add up correctly. One would think that the 75th anniversary would occasion the 76th GA. As you suspected, there were two "special" GAs that convened beyond the normal summer sequence of meetings.
The first was in November 1936, when the GA held its second meeting, five months after its formation, for the purpose of approving the constitution of the church. This was no mere ratification of Westminster Confession, but it also involved a determination of the text of the confession. Specifically, would the new church accept the revisions of 1903? Despite some support for that approach, the church determined not to accept the 1903 revisions in the version of the Confession that it adopted.
The second took place in February 1939, when the young church, at the time called the "Presbyterian Church of America," was threatened by the PCUSA with a lawsuit for trademark infringement with its name. The consensus in the church was that it lacked the financial resources to engage in a long and contested legal battle. So this special assembly had the sole agenda of selecting a new name, and it chose "Orthodox Presbyterian Church."
So, two special General Assemblies. And that is why the 78th General Assembly celebrated our 75th anniversary.
February 15, 2022
December 21, 2021
July 24, 2021
May 15, 2021
May 06, 2021
December 04, 2020
October 29, 2020
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