I’ve just stumbled on this thread and thought I should defend Genesis’ honour a little:The whole "BUY THE MISSING DISC" is a really cheap and low blow-the least they could have done is include a coupon for a hefty discount if you wanted it.
The Live Over Europe disc was released before the box set was planned. But when the box set was released, it was only in the recent past, so they didn’t want to include it, knowing that the fans had only just bought the disc as a stand-alone item. They made an extra space in the box so that fans could put their previously bought disc in the box. So from that point of view, they were (trying to be) being nice – not making people buy the disc again, but making space for it in the box. I agree, though, that a voucher for a discounted version might have made sense (but might have annoyed the early adopters).
Side four of the regular edition is studio recordings. Then there was a limited supply of that album called "Four Sides Live", with the fourth side being live recordings. It has the same album jacket as "Three Sides", but an orange sticker shaped like an exclamation mark, covering the "Three" in the title with "Four".
I was fortunate enough to get one of these at a flea market some years ago. Paid 5 Euro for it.
The CD has it complete, studio and live tracks.
It was called Three Sides Live in the UK even though we got the 4 live sides as standard (the non-UK studio side tracks were all UK B-sides). That used to confuse people even more. I don’t think there has ever been an issue officially called Four Sides Live – interesting to hear about the sticker, I assume the labels still said Three.