The Scottish Boinc Team

Do some PCIe slots not have the retainer clips? I have a few mobos with slots that look like PCIe but without the retainer clips. The mobo manual says they are PCIe, not PCI. Info?

Yep some have none, especially PCIe Gen2 x1 slots -such as e.g. on the Raspberry Pi Compute Model I/O Board- they are the shorter PCIe slots you find on your mobo.
The longest ones usually have a retainer clip.