The failure of a comprehensive combustion system analysis CSA intended for application to both rich and lean domes to predict a priori the impact of TAPS’ tips and pilot’s design features on low-power flame characteristics as well as on high-power NOx emissions led to reassessment of the roles that empirical know-how, CFD, rig and engine testing play in developing combustion technologies and products since the early 1970s acknowledging how strongly the underlying hypotheses influenced both the technology and product development process. Deep dive into the technology and development activities since the mid-1970s led to the conclusion that successful hypotheses are closely connected to the low emissions characterization process which needed to be updated for the two generations of rich-dome, and lean-dome combustion products in addition to TAPS2, TAPS3, LDI-2 and LDI-3 combustion technologies, as described in this paper. Moreover, this effort needs to bring in the most recently certified engines’ non-volatile particulate matter, nvPM, database as part of the emissions characterization process. NASA’s National Combustion Code, NCC, after calibration with the LDI-1 NOx emissions database was used successfully for defining LDI-2 and LDI-3 technologies. But it needs to bring in further improvement regarding low-power operation and operability, the subject under investigation by the authors since 2015. The fundamental understanding of the critical processes, especially on operability of LDI, is summarized in this paper including integrated diagnostics and CFD modeling activities.