My expectation is that dev kits come in three stages; pre-silicon, early silicon, and final silicon.
The first pre-silicon dev kits would use existing hardware that's reasonably close in architecture and performance to what's expected from the final hardware. For a new Switch model, this might be a Xavier-based dev kit, with the CPU clocked down and maybe a few cores disabled, and potentially with a discrete Ampere GPU attached. I would expect Nintendo to communicate the actual specifications to developers alongside this, with non-final clocks, to give devs a performance target to aim for.
The early silicon (aka engineering samples) dev kits would be available post tape out, when the first silicon is available for testing. These dev kits would be effectively final, although with clock speeds which could change prior to launch, depending on binning of final silicon, etc.
The final silicon dev kits would only be available very near to launch, or potentially even after the launch of the console. This is what would be used for the rest of the console's life, and would obviously 100% match the actual hardware.
I would expect developers to currently have the first type; pre-silicon dev kits. It's important to note that starting development for a new console doesn't require final hardware. An early dev kit allows developers to get up to speed with any new APIs or software tools, and to work with the new architecture and get a feel for how to optimise around it, and the final hardware specs given alongside this would allow the developer to know what kind of performance to target. So long as the actual performance is in line with what was promised by the console maker, it should then be pretty straight-forward to get it running on final hardware. It's also not unusual for these dev kits to be available long before the hardware itself. The Wii U, for example, was announced almost a year and a half before release, and dev kits based on the Radeon HD 4850 existing even before that.
I should mention that I have no direct experience with any of this stuff, but having followed along with this stuff for quite a few years now, the three stages above tend to be the standard pattern of things.
Thanks for the clarification. Although the main quotes from the article are from... this thread, so I'll still err on the side of caution with this one.