Macbook Pro 2011 - logic board replacement programme

Your 2011 computer is obsolete or vintage, Vintage and obsolete products - Apple Support

Your computer was not upgraded to a new year because your logic board was replaced. newer model logic boards do not necessarily fit into older model computers.

Designer Gav UK wrote:

can still go with OS Catalina if the actual insides are still 'under age' so to speak!

2012 is the cutoff for MBP—your 2011 does not have the Metal-capable GPU hardware.

macOS Catalina - Technical Specifications - Apple Support

https://support.apple.com/kb/SP803?locale=en_US

MacBook: Early 2015 or newer

MacBook Air: Mid 2012 or newer

MacBook Pro: Mid 2012 or newer

Mac Mini: Late 2012 or newer

iMac: Late 2012 or newer

iMac Pro

Mac Pro: Late 2013 or newer; Mid 2010 or Mid 2012 if upgraded with a recommended Metal-capable GPU

<<... surely Apple wouldn’t replace it like-for-like 4 years later? >>

That is EXACTLY what they did, except that the one they removed had a problem, and the one they installed had that problem fixed.

It is still a 2011 model, and is still supported to run 10.13 High Sierra without any issues.

There are some hobbyist hacks that can allow it to run most features of later versions, but they are strictly "use at own risk, including risk of 'brick'-ing your Mac".

You understand correctly.

But all the "stuff" that needs to change is on the logic board. Your logic board, even if replaced four years later, has the same components of every other 2011 MacBook Pro like it.

Logic boards are custom made for each model year. Ones from a different year are unlikely to fit, unlikely to work properly, and unlikely to cool themselves properly. Changing to a different model logic board is not commonly even attempted.