You are referring to the publication of Travis et al, 2017 in which they established the new reference range taking into consideration the testosterone assay calibration efforts by the CDC.
Let me try to explain
The previous ref range that eg LabCorp used was 348 - 1197 ng/dl. Thats based on an LC-MS method using the data from the Framingham study (Bhasin et al, 2011).
The new reference range is 264 - 916 ng/dl. And thats based on the study from Travis et al., 2017 which used data from 1185 healthy nonobese young men. It also used LC-MS technology and used samples from 4 different cohorts the Framingham samples was one cohort).
Now where does the difference come from?
In short, about 90% of the difference comes from the fact that a newly established calibrant was used to calibrate the results from the different studies to the CDC standard.
About 10% comes from the fact that non obese (BMI <30) young males were studied in the Travis study whereas lean young men were used in the Bhasin study.
In more detail. Different testosterone assays have different responses. They give you different results when measuring the same sample. The assays need to be calibrated if one wants to compare different samples from different labs. Thats why the CDC came up with a testosterone assay standardization program. The study by Travis et al is the first study which made use of the newly established CDC calibrant.
Take a look at figure 1 of Travis 2017, second row. The exact same samples from the Framingham study (FHS) were re measured again using the new calibrant and compared to the original results. You can see that an average of difference of 144 ng/dl nwas found.
In other words. If you had your blood analyzed at LabCorp before 2017 and the result was 600 ng/dl and you had the blood froozen and reanalyzed now the result would be around 450 ng/dl (again Figure 1, 2nd row right shows the correlation between the old (FSH) data and the new data).
The reference range changed predominantly due to the calibration of the T assay to the CDC standars and not because the population testosterone declined.
Again i am not saying that the population T is not declining, in fact I personally believe they did, but the data is ambiguous.
I hope this ensures you that nobody is intentionally falsifying any T measurements to neglect treatment for low T.
Figure 1 from Travis et, 2017