Due to the way Android reads Build.Model information, there is no way to determine D820 vs. D821 models for the Nexus 5 (reports "Nexus 5"). Currently the data source will report D821 information all the time (even for a D820 phone). Not sure what the fix here will be due to the fact that the same Android firmware is used for both models, so there is no unique information to identify the model number. Thanks to @aksimhal for the information!