Looking on the internet deeply has found these results:

the book he bought was is the most popular phrase on the web.

the book he had bought was 10 results on the web	the book he bought was 118 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	If it is added an agent like The book he bought was lost, inversely , this explanation also take effect as English prototypical agentful passives that�he� becomes�... Oct 14, 2013 ... You are right, in fact I read the book he bought was on blackpowder Colt revolvers. And for the record there were fluted cap and ball original�... The book he bought was not the book he intended to buy' (not' he mistakenly bought a book.) (10b) He bought the wrong book. 'The book he bought was not the�... Jan 9, 2008 ... "The book he bought was about [American] Indian spirituality, and he got one for both his mother and brother, who are ministers. His mother�...

the book he had bought was

10 results on the web

the book he bought was

118 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

If it is added an agent like The book he bought was lost, inversely , this explanation also take effect as English prototypical agentful passives that�he� becomes�...
Oct 14, 2013 ... You are right, in fact I read the book he bought was on blackpowder Colt revolvers. And for the record there were fluted cap and ball original�...
The book he bought was not the book he intended to buy' (not' he mistakenly bought a book.) (10b) He bought the wrong book. 'The book he bought was not the�...
Jan 9, 2008 ... "The book he bought was about [American] Indian spirituality, and he got one for both his mother and brother, who are ministers. His mother�...