Even if you have installed every security patch up to the current date, the system still reports the base build 16.0.4266.1001. The Secret Check:
16.0.4266.1001 Architecture: 64-bit (X64) Edition: Volume Licensed (Pro Plus) Microsoft Office 2016 Pro Plus 16.0.4266.1001 VL X64
As the most comprehensive edition in the 2016 lineup, the Professional Plus suite includes: Even if you have installed every security patch
Volume License (VL) via MSI (Microsoft Installer) Microsoft Office 2016 Pro Plus 16.0.4266.1001 VL X64
Real-time communication for enterprises. Key Features of the 2016 Release