Do not read until you've seen the 2015 Doctor Who Christmas Special!

There are spoilers!

Wait until you've seen it please.  Or you can read this anyways because you want to know about plot hole stuff.

Spoilers!

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So at the end of the episode, they go to the singing towers of Derillium for the last time together.  Well, the first and last time.

The 11th Doctor already took her there for the last time.

They made this mini episode that was a two parter.  It was called The First Night and The Last Night in the Night and the Doctor series.  

There the present version of the Doctor bumped into the future version of 11.  The future version told current 11 that he was taking River to Derillium  and that it was time for River to head to her death after that.

Maybe that just could have visited multiple times but if 11 thought it was time, he would have had her sonic ready so 10 could save her to the library.  However, we see 12 giving River her sonic.

River said that they had tried going many times before but he kept canceling.  This time 11 seemed pretty sure he was going to go through with it.  But that might have canceled again.

Maybe this plot hole isn't quite as bad as some others but it still adds to the collective plot hole known as River Song.

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Merry Christmas!  Or happy holidays is you don't do Christmas!