The price of the original Silverbird release should be £1.99 rather then £3.99 according to these reviews:
Sinclair User: https://spectrumcomputing.co.uk/mag.php ... 84&page=61
Your Sinclair: https://spectrumcomputing.co.uk/mag.php ... 62&page=50
If the Code Masters re-release actually happened, which seems unlikely, then the year should be 1993 and the price £3.99 not £1.99 according to these reviews:
Sinclair User: https://spectrumcomputing.co.uk/mag.php ... 21&page=19
Your Sinclair: https://spectrumcomputing.co.uk/mag.php ... 95&page=18