Rein it's unknown where they originated from, the testing was done by law enforcement from confiscated steroids I believe so there would only be speculation as to the source
It's published in the Journal of Analytical Toxicology and I believe the study is/was:
Analysis of Confiscated Black Market Drugs Using Chromatographic and Mass Spectrometric Approaches
Mario Thevis*, Yvonne Schrader, Andreas Thomas, Gerd Sigmund, Hans Geyer, and Wilhelm Schanzer
Center for Preventive Doping Research--Institute of Biochemistry, German Sport University Cologne, Carl-Diem Weg 6,
50933 Cologne, Germany
The study abstract:
In the context of house searches in Germany, numerous drugs
were confiscated and subjected to chemical analysis, including
anabolic agents such as various anabolic-androgenic steroids
(stanozolol, testosterone derivatives, trenbolone esters, etc.) and
clenbuterol, as well as agents with anti-estrogenic activity
(tamoxifen, clomiphene), drugs stimulating virility (sildenafil,
tadalafil), and unlabeled plastic bags. Liquid chromatographytandem
mass spectrometry, gas chromatography-mass
spectrometry with nitrogen-phosphorus specific detection, gel
electrophoresis, and immunological tests were employed to test for
the effective content of 70 products. In 18 cases (25.7%), the
declared ingredients differed from the actual content, in particular
concerning anabolic-androgenic steroids. Nandrolone and
trenbolone esters, for instance, were frequently substituted or
complemented by various testosterone derivatives, and several
testosterone depot formulations originally composed of four
different esters were found to contain fewer or wrong components.
Except for those drugs supposedly originating from so-called
underground labs, fake packings were hardly or not distinguishable
from original boxes by visual inspection.