Thanks to Peter Weighill for highlighting, but the World of Spectrum have recently recovered another unreleased game, this time an early version of Basket Master called Fernando Martin Basket Master
Now, this particular version was in development with support by Dinamic, but the owners decided that deadlines were being missed and the game was reassigned to another programmer. The game used the graphics that were already created, but the new programmer did the game code itself from scratch. Apart from a mention in Micro Hobby magazine in 1986, the original BETA version has never surfaced until now.
It begs the question now if a similar fate happened to C64 and Amstrad conversions, with the C64 version being done I think in-house by Gari Biasillo.
But for Spectrum owners, check out the findings and read more details over at the WoS entry here: