1959 to 2026. The Spectrum went out of production in 1992 and the catalogue has not stopped since.
1905 is almost certainly wrong. Screen Stars is a 1988 game, and this is the only year in the catalogue outside 1959 to now. It is missing in action, which is a fair part of why nobody has corrected it.
17,001 entries carry no year at all , which is more than any single year holds and about 38% of the catalogue. Most of that is simply not known, but 475 were announced and never sold, so they have no release date to record, and 647 are known only by reputation, with no copy ever found to date.