@kdfrawg They’ve fucked up & are too bloody arrogant to admit it.

//

This might help you to get your Mac working again on Sierra:

// @kdfrawg

feecb99c-6ba3-4142-b6bb-2b597d5aa944

With no way to get back if their Time Machine backups were not complete ones, as yours were not. With a proper backup you can revert.

// @kdfrawg

Yes, I have just noticed this. But in my case, I make a copy of the installer after it's downloaded & before I start the installation.
You mentioned your Time machine restoration didn't include the OS? Did you make partial or full Time Machine backups? I have always tried to make full backups, a few years ago TM was cranky on one Mac & only did partial ones for about six months before a new OS install fixed it up.

//

So far, I have.

Sierra should still be available on your purchased list.

/

My mate hates it when I put his chocolate bars in other chocolate bar wrappers.

It gets his Snickers in a Twix.

Boss: "You've been late three days this week, do you know what that means?"

Me: "It's Wednesday?"

If America switched from pounds to kilograms overnight, would it create mass confusion?