Maybe they’re something like the Frisbeterians that believe your soul is like a frisbee. When you die, it goes up on the roof and you can’t get it back.
I don’t know but many of those denominations - the PCA, the OPC, the RPCA, and some of the others - share standards that mean an ordained man or a church member can move back and forth between the denominations with little fuss, based on whichever variant is close by. The differences amount to historical and geographical identities that the denominations don’t want to give up.
The only ones one the list you mentioned that I don’t think count for that is the EPC, which is newish and has some issues (I think they ordain deaconesses) and the Cumberland folk who I believe are Presbyterian in form of government but not reformed in doctrine.
Evangelical Covenant Order Of Presbyterians
The latest spinoff off the crumbling mainline PCUSA. It's been discussed on FR before. The breaking point this time was homosexual ordination.
http://www.fellowship-pres.org/eco/.
I noted when it first came out that it was easier to find a schedule of employee health insurance costs for them than a firm statement of belief.
The “Covenant Order of Presbyterians” is basically for Presbyterians who are against homosexual ordination, but are fine with requiring Churches to have female ministers and elders(leaders).
Of the more conservative Presbyterian groups (PCA, ARP, OPC), only the Evangelical Presbyterian Church (EPC) allows female ministers or elders, and then, ONLY if a congregation elects to have them (and most congregations don’t...). Hence ECOP is basically what the mainline PCUSA was say, 30 years ago.
It is also unique in that it has 2 levels of membership, in that mainline churches can stay PCUSA, but be associated with ECOP, or they can elect to leave the PCUSA (and very likely be sued for their building...) and directly join ECOP.
Basically designed for feminist evangelical-(lite) Presbyterians.