ok, so the OPC broke from the PCUSA, then the PCUSA became the UPCUSA and the PCUS. The the PCUS broke into the PCA and PCUS. Then the PCUS and UPCUSA joined to become the PCUSA. Meanwhile the OPC split into the BPC and EPC. Ouch!
And, in 1982 the PCA and the Reformed Presbyterian Church Evangelical Synod (RPCES) came together in a process called “joining and receiving” whereby all the RPCES churches with their officers became members of the PCA. Thus the PCA is the conservative result of two prior groups coming together, one mainly Southern and the other mainly Northern.