Plots are odd things, hard to tie down. They always seem to want to shift as you make them. No sooner have you finalised things absolutely, definitely for the last time (honest) than it occurs to you that things might work better the other way around.
They're also an area where people (by which I mean me) sometimes avoid thinking about the weaknesses in them. Sometimes I'll go around several rounds of edits wondering why a story is flat, changing small things, playing with dialogue, or characters, or description, or anything but the bit where the problem actually lies.
One of the stranger things about the ghostwriting is that I get the plots fully formed. That creates tremendous freedom to concentrate on those other aspects, but it also creates the need to stamp very heavily on the urge for things to change as you go. That's actually a good thing, sometimes, given how easily I can wander off track with these things.