This is an oddity really, though I guess there would've been quite a few spares leftover when Sinclair ended up in financial stife and sold out to Amstrad.
This is a version 6 motherboard for the 'toastrack' 128K speccy, the last one
Sinclair produced. When it was launched in Spain (where it was manufactured)
it included a numeric keypad, a feature that was dropped from the UK version
probably because of cost. Interesting to see the port still available on the
board though, and even more interesting to discover that both the port and the ROM code lived on until Amstrad released the +2A.