PCIe is extremely flexible. Often times those big 16x slots are actually only wired for 8x or even 4x. The device has to be able to support running on fewer lanes than expected because of stuff like this.

Well, its basically running at PCIe 1x. Thats why theres all those notches on the full 16x card. You can install in a 1x, 2x, or 4x header, and it will work. Problem is some cards dont have the notches and need the full connector, but supposedly you can grind off some plastic from the port to make it fit and it will still work.

Also this is PCIe, not PCI. It's just got a few gaps because it's actually only x4, and the other pins are just there for stability.

You don’t even need to tape them up. The slot is open ended explicitly for this kind of situation. The extra contacts just dangle and have no power running through them since they aren’t connected.

I don’t think I’ve ever encountered a pcie card that will not function at all unless it receives it’s required lanes

One of the few things that'd be problematic would be the x16 -> quad M.2 cards which use PCIe bifurcation.
Lanes 1-4 from the socket are wired to the first M.2, 5-8 to the 2nd, etc.

It would still work (by some definition of the word), but in the sense that the first M.2 drive would get 1 lane and any others wouldn't be connected.

(Quad M.2 boards with a "PLX" or other PCIe switch chip would work fine with 1 upstream lane serving all 4 drives)

If you put your bootloader with nvme support on a recognized drive it works.

The original ssd was rammed full, only about 20GB free. Writing files was super fast - it was mainly reading files that the SSD struggled to do at a palatable speed, often locking up my pc for a few seconds

With the new SSD i've just left the remaining space unallocated, so it's firmware can freely use that space for whatever it needs to 😁

Price mainly, and I wanted something that wouldn't be constrained by a 1x lane in another mobo in future

Ive got a few 1x cards. For example, my old home server box has a 1x slot that you can plug in a 1x gpu, or additional networking card, USB, etc.

Lol. You can shove all sorts of crap in those.

No. The back end interface is pcie instead of sata.

Is NVMe really cheaper? I thought SATA was the cheaper one.

I had a (slightly old) image backup just in case, thankfully didn't need to use it though!