The first is a requirement that drug tests administered under the provisions of the WADA Code need only be stored for a minimum of 3 months. That includes positive tests - adverse analytical findings in WADA's jargon. This explains why the samples taken from Steven Colvert were destroyed long ago. Had they been saved, resolving his guilt or innocence with more advanced drug testing methods might be straightforward today.
There is an exception (220.127.116.11):
If the Laboratory has been informed by the Testing Authority that the analysis of a Sample is challenged, disputed or under longitudinal investigation, the Sample shall be stored frozen and all records pertaining to the Testing of that Sample shall be stored until completion of any challenge or investigation.Any athlete, like Colvert, who believes that an adverse finding has occurred with respect to their urine or blood sample should -- as a matter of procedure -- immediately challenge or dispute the finding in such a manner that requires the sample to be preserved.
More generally, it should be a general policy that all samples associated with adverse analytical or atypical results is stored for a lengthy period, such as 10 years.
What would this involve?
All Olympic drug tests are stored for 10 years, in hopes of finding future evidence of guilt among dopers who initially escaped detection. At the Rio 2016 Summer Olympics this totaled about 5,000 tests, according to reports. Compare this with 3,866 adverse and atypical findings across all drug tests administered by WADA-accredited laboratories in 2014 (here in PDF). The scale would thus be similar to what is already done.
A second significant regulation in the lab standards is the reversal of burden of proof upon an adverse analytical finding. This means that upon a positive drug test, WADA "presumes" that the test is accurate and at that point the burden of proof is upon the athlete to prove that the test is flawed.
Here are the relevant passages from the WADA standards:
Fortunately, most criminal justice systems do not work this way. However, anti-doping regulation does.
The combination of destroying evidence on which convictions are based after only a very short time and the reversal of the burden of proof dramatically increase the odds that athletes innocent of doping will become wrongly accused and sanctioned. Athletes should demand that both of these regulations be changed.