I don't think it's possible legally to go after old breaches with new rules. The rules at the time of breach are applicable. At least here.
Sure you can. Firstly what you would be punishing is current failure to disclose past offenses, not the offenses themselves.
While I agree with the sentiment of your post, I still reckon it would be hard, with little returns, going down that road. But let's do the thinking.
To be able to sanction "failure to disclose" you would need to do formal interrogations with a rider first. (You can hardly sanction a rider's past denial of doping to a journalist. CF Armstrongs books considered protected by freedom of speech in court) But even so, refusal of testimony is a constitutional (or amended) right in many places, and sporting rules can not restrict your constitutional rights. So what is the incentive to come forward? In the end you have pissed off a lot of people, and bullet proof evidence against a very little number.
(Not a lawyer, just MHO, feel free to take this post apart)
Firstly the below is in no way trying to "take your post apart"...its just my point of view wrt yours.,,
Respectfully, I think, honestly, you misunderstand the role of a Truth and Reconciliation (T&R from here-on), as well as how it works. Firstly you have to separate between Criminal Proceedings (the state wants to find you guilty and put you in prison) and wider Tort Law Civil Actions- (you've done something bad to me and I want you to pay me)...T&R would come under the second, where things like the onus of proof and the right to silence are not given the same weight as in criminal proceedings. (Interestingly, apparently the Napoleonic code under which most of European Law was written does not reckoning the same "innocent until proven guilty" and the pursuant right to silence, but I digress). Ideas such as upholding constitutional rights do not come into it, IMHO, as you're not taking anything away from someone - simply making a potential employee/racing license holder pass some "standards" which are above the scope of criminal law.
An example in real life is an employer may require you to take a drugs test prior to taking up employment, whereas Police officers in many countries are not allowed to ask for drug tests unless there are legal suspicions. Personally I would take failure to appear before the committee as an admission of guilt but that's just me, in any case you wouldn't have to REQUIRE riders to appear, all you wold be doing is to say to a rider "anything that was NOT discovered in the T&R process and is found out later
results in you getting a lifetime ban", and with ex-riders naming and shaming as much as they are Id have thought a current rider who had doped would be crazy not to get ahead of the pitch.
Id totally not bother interviewing past "stars" like Armstrong unless they wanted to renew their racing license, the ethos of this is setting the clock back to zero NOW, not correcting past wrongs
You would ABSOLUTELY have to take depositions from all current riders, coaches etc, on the understanding of confidentiality (ie no writing a book after it) and a one off immunity from sanctions. 99% of the purpose of the T&R would be to draw a line under any past indiscretions and start anew (the other 1% would be to learn more about how dopers got away with it to tighten the current processes). Once again, the quintessence of this process is to say, to riders, teams, sponsors and to the public, "ok, for once and for all we are starting afresh"
...note that, as I said earlier, I believe this process is pretty worthless if you were then to continue with punishments ranging from a "suspended from competition" to a "max 2 year ban which most country associations seem to adhere to.
This is by its very nature a very expensive process, cumbersome as you've got national associations protecting their own interests, but its kind of what the UCI is there for..