Doc0075: In the Spectrum version there was a bug which would lead to instant death when you entered certain rooms.
Ghorpm: Ah ok then. I think the hardest thing would be to beat them on the same day. Why you may ask? Especially because JSW2 uses the same rooms as JSW and just adds some more (a lot more but still). But the jumping mechanism is different: in one of the them you simply jump forward but in the other Willy is always taking a step forward and only then jumping. That makes it completely different. You can not jump for the very edge of a platform in one game while it is required in the other. Takes some time to get used to the other game
I think in JSW 1 on the C64 if you jumped right you went a shorter distance than if you jumped left, making it difficult to complete some screens. The aim of JSW 2 was to fix some of the major problems in the game, plus milk some more money out of people at the same time.