Apple trade-in page

Apparently they aren't. Even when I select the correct CPU there are still other unknown variables…

"The iMac "Core i7" 4.0 27-Inch Aluminum (Retina 5K, Late 2015/Skylake) features a 14-nm "Skylake" Quad Core 4.0 GHz Intel "Core i7" processor (6700K) with four independent processor "cores" on a single chip, an 8 MB shared level 3 cache, 8 GB of 1867 MHz LPDDR3 SDRAM (PC3-14900) installed in pairs (two 4 GB modules), a 1 TB or 2 TB "Fusion Drive," and an AMD Radeon R9 M390 or AMD Radeon R9 M395 graphics processor with 2 GB of dedicated GDDR5 memory. It also has a built-in "FaceTime HD" webcam and stereo speakers."

One reason would be a serial number can refer to more than one device. For example, if I plug in the serial number for my late-2015 iMac into everymac.com's serial number lookup, I get three different iMacs to choose from.

Oddly, when I enter my serial number on Beetstech it accurately recognises my device as a 2019 27-inch Retina iMac … enter the same serial number on Apple and it gives me a series of questions where my only year options are from Late-2013 to Late-2015 or Other, none of the HD sizes match my device, and then it tells me my device is ready to be recycled!

I get four options when I plug in my iMac Pro, each one of which has other options.

You're welcome. Some serial numbers may in fact be unique. At least only refer to one specific device with a certain set-up. That I can't say.

Tom Wolsky wrote:

So if an institution buys a bunch of similar computers they’re likely to have machines with the same number.

It seems so.

Here's some further info about Apple serial numbers. What they aren't is a way to identify a unique device.

https://beetstech.com/blog/decode-meaning-behind-apple-serial-number

You're welcome.