I flushed out my Price-To-Trend-Book-Value thoughts a bit more in this post:...

Though I think it's a remarkable fact that book per share has trended so well over the years, I would URGE people not to use the trend line for prognostication.
(nor consider the ratio of current price to long run trend line as having any meaning).

The fact that the figures have trended so well should be considered a cute coincidence, and also a remarkable complement for management on what they have accomplished...in the past.
But the value of something is what it will do in future, as estimated from what's visible today, not what it would have been if an old trend had continued.

For an excellent example of the problem, consider the UK economy recently : )
economicshelp.org - Britains recovery strong weak
It would not be wise to see the huge gap below prior trend as suggesting that the current values are temporarily low.

In short, the trend might not continue.
And to the extent that it might, recent typical results build better extrapolation than the long run trend, because it's at least based on today's reality.
The results in the 2000s and 2010s say pretty much zip about what's going to happen in the next decade.

Jim