The Windows 10 versioning uses a YYMM format and version 1507 reflects the original JULY 2015 release.  After March 26, 2017, the original release will no longer be updated, as reflected below.  This issue will primarily impact corporate WIN10 versions — as this is the only eligible version, where users can easily turn off updates

http://www.zdnet.com/article/reminder-microsoft-to-no-longer-update-original-windows-10-release-after-march-26/

IT pros running Windows 10: Update your engines.  As Microsoft noted last year, the company plans to update only two Current Branch for Business versions of Windows 10 at any given time.  Now that Microsoft has released the media for its Windows 10 Anniversary Update — the Windows 10 bits that it released in August 2016, plus a Cumulative Update to it from late last year — the time is winding down for the original version of Windows 10 released in July 2015.

The first release of Windows 10, known as 1507, is the version that Microsoft will no longer update after March 26, 2017. The other two versions of the product in market — the November update (1511) from November 2015 and the Anniversary Update (1607) — will continue to get regular security and feature fixes and updates.