How do I know which printing of the PHB I have?

Question

There are differences among printings of the Player's Handbook which are not captured in the errata, as came up when recently discussing Druidic Foci and Arcane Wards.

How do I know which printing I have? How many printings which incorporate changes have there been? As some of the differences aren't identified as errata, is there a sense as to whether one printing or another is controlling?

I'm envisioning a situation at a table where two players are looking at the same page, seeing different text, and there's no mention of it in the errata. How to even know which is more-recent?

Answer 1

Somewhat oddly, your question is answered by the Sage Advice Compendium document which was first released as part of a Sage Advice article by Jeremy Crawford on the official D&D website entitled Rules Roundup.

This document says the following on the first page, under the "Errata" heading:

A corrected version of the book includes the following text toward the bottom of its credits page:

This printing includes corrections to the first printing.

At the time of writing this answer, there have only been two printings of the Player's Handbook: the original, and the latest which incorporates the errata updates. Any rules clarifications which are not considered errata are going to continue to be found in the updated versions of the Sage Advice Compendium document. The latest version is always accessible from the official D&D website, and includes a version number both in the file name and in the footer of the document. The latest version always takes precedence over previous versions. Note that the errata document can also be distinguished from later updates by its version number, which is also contained in the file name as well as the footer of the document.

Answer 2

Look at the Copyright page. Near the bottom, under where it says "First Printing: August 2014" is a string of numbers, like "11 10 9 8 7". The last number in the string (or the first, if it counts up instead of down) is the printing number. My copy reads "9 8 7", so I must have the seventh printing.