<<Why did Marvel continue the book for 5 years as a reprint book instead of canceling it outright?  <<

I had heard that the sales numbers for the Neal Adams run actually shot up AFTER the book had already been cancelled, but it was too late to keep the creative team, who had moved on - so keeping it as a reprint was in part, a responce to sales but lack of creators.

And, as noted, with minimal costs, the break even probably didn't really even shift much!

I would guess that Classic X-Men, starting in the mid-80's, was probably the last successful reprint title.

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That book was my first proper introduction to the X-men.  Just after it first came out there was a group of us staying at a friends house.  He had a huge stack of 'American' comics (the only ones I new here were the weekly Marvels - which I didn't know where reprints) the top of which were Classic X-men 1-5.  While everyone slept I read them all in one go, my own little secret world. 

When I got home later that day got out what little pocket money I had, trecked off to the local news agents and got Uncanny X-men #219 and X-factor #18.  At the time I didn't know who the 'real' group was as I wasn't aware of the span of time involved between what I read that morning and what I just got.  Even though the word 'Classic' was in the title, I didn't know it was referring to reprints, with a back-up story.  To me it was a two part story each drawn by a different artist.

Those were simpler days back then, 

(In HIDDEN YEARS I planned to explain the switch in context. Had already begun to set it up, in fact, with Jean's reversion to her original uniform.)

One of the things that was fun about XHY, of course, was that being set in the Past it was bound to neither real time nor "Marvel time". I could put as many issues of my book between those extracurricular activities as I wanted!