While HP does not specifically evaluate against the STMC standard, HP does assess product packaging integrity, image density, background, and estimated yield.
Packaging integrity is assessed under HP's own internal standard which at a minimum meets ISTA 1A. Cartridge yield is evaluated in accordance with ISO/IEC 19752 and ISO/IEC 19789 and made available at http://www.hp.com/pageyield/. Image density and background are measured with industry standard devices that meet ISO 17025 specifications for accuracy and repeatability.
The definition of STMC can be found here: http://www.i-itc.org/stmguide.htm