Wow thank you to both of you for the insight, really appreciate it It was something I have wondered about for a while as I absolutely love the massive pixel perfect maps that were in many of the old game magazines, to me it's a work of pure art.
Do you happen to know any additional information about the frame capture devices? They sound like a really interesting piece of hardware!
I downloaded Nintendo Power issue 1 and see exactly what you mean when I look really closely I can see the stitch lines you mentioned on Double Dragon and even Mario:
I'm guessing the later issue started to use the hardware or developer contacts to get the images as they seem a bit cleaner
I'll look for that Player One Podcast with the former EGM editors thanks for letting me know.
I didn't realise some games had a debug mode where you could scroll the whole level, do you happen to know which games they were?
That's a very good point about the repeating texture/tile data it would be easier than I initially thought because they can find out where the tiles line up and edit accordingly.