Do I need a recent book on QGD Tartakower or Lasker as Black, or is Sadler good?

The Ntirlis book is certainly not for beginners but is half way a middle game book with the main lines having a explaining ideas chapter, followed by a chapter on the theoretical lines. For example the sections on the exchange variation, explain some of the typical ideas in that structure. There is also one specific line in Kramnik's improved orthodox h6, Nb-d7 and c5 that is covered which transposes to the tartakower. I am not very sure, what is supposed to be white's most testing approach in tartakower, but the line mentioned is one of the better ones.

In his book Ntirlis gives a specific opening line in Chapter 1b, which, as he puts it, "angles" for a Tartakower setup.  He calls it the Romanishin Variation of the Tartakower Defence.  He also provides several example games featuring the line (pp.34-41).  However beyond that there is no other coverage of the Tartakower Variation of the QGD (that I am aware of - I haven't scoured every last page of the book!).  

These are the featured example games he annotates.....(they all end in draws)...

Ahmed Adly vs Vladimir Kramnik, Baku Olympiad 2016

https://www.chessgames.com/perl/chessgame?gid=1832619

Jernej Spalir vs Tigran S. Petrosyan, Katowice 2014

https://old.chesstempo.com/gamedb/game/3650274

Ivan Cheparinov vs Michael Adams, Plovdiv 2010

https://www.chessgames.com/perl/chessgame?gid=1598662

  How do you find anything in that book? I find it frustrating because it is full of interesting ideas but so disorganized.

I just wanted to thank you and @TwoMove again for this recommendation. I ended up buying Ntirlis and have studied it every day since. Each chapter is clearly laid out presenting the important ideas, the repertoire feels consistent, and the entire book seems very well-researched. The balance between theory and brevity was perfect for me.

I'm glad it's working out well for you. I read the entire Semi-Slav Grandmaster Repertoire book and I hardly ever touch the mainlines. People really like their sidelines