By the way, these tax changes you don´t see at a historical P/B chart. ;-)

You do in a way--
when the tax rates dropped in 2017, book value jumped upwards because the deferrred tax liability (largely from appreciated stock positions) was suddenly much smaller.
The stock price had risen strongly through 2017 and into early 2018.
As the stock price weakened in the first half of 2018, but the P/B fell a LOT (1.7 to 1.34) because known book jumped upwards on the release of the year-end report. I presume the market ran the stock up before that because it was known that the value of the firm (and book) were about to rise, then the financial reporting period lag caught up. So P/B was "artificially" high for a brief stretch around year end 2017 - after the market reaction but before the financial reporting caught up.

Jim