UK gaming magazines of the day are really hazy, because obviously having watched the system be delayed for two years, they started talking about import titles, I.e. when were things released in North America or Japan (and priority was still on Amigas/Atari STs). My understanding is that the system was delayed a few times - it was originally penciled in for a Q1/Q2 1990 release (about March/April time, possibly even in 1989 at some point) but was pushed back due to manufacturing problems.
Nobody really talked about the system before 1991 because it wasn't a 16-bit computer, but there's a few clues
supposedly the Mega Drive was due to launch in the UK in September, at the "European Computer Entertainment Show" (ECES) which no longer exists and is poorly documented. That year it was held on September 15th-16th, which from what I can see, was a weekend (so sometime between the 17th and 21st? I hear Fridays are big days for gaming in the UK (like Tuesdays in the US)). It's also the same period in which the Game Boy launched, supposedly (Wikipedia says the PAL release for that was the 28th - a Friday)
Anyway things I know
- £189.99 would get you a console with Altered Beast. That makes Altered Beast a launch title, obviously
- Games were released in October and November - there are only 30 days in November, so if the internet is right, that makes all of them launch titles. That's why I think the internet is wrong
- Space Harrier II and Super Thunder Blade were sold as "budget" games for about £10 less than normal, on the basis that they were older (1988 in Japan)
the other issue is that obviously "Europe" as a region isn't very... precise (or at least, it wasn't in 1990). The United Kingdom release was likely different than the French or German or Spanish one - different distributors, language barriers, logistical issues etc. This is certainly the case with the Master System - I'm curious to know if it affects the Mega Drive significantly too.
it's difficult to find concrete answers - it was a world dominated by Amigas and Atari STs. Dedicated consoles were seen as niche systems for kids - real men messed around with 329343289342 floppy disks and broken cassettes, so this stuff just wasn't covered. Or at least, not until Sonic turned up.