It is very common to breed male studs at 1 though many would be very concerned at breeding them younger than that when they are still technically puppies.
The problem with doing this in cavaliers -- and why there cannot be any justification in doing so (after all, if a boy cannot figure out what goes where even if he hasn't been bred, doesn't that suggest a problem?! I know older neutered dogs only too happy to give a game girl a try and they have never been bred!) is that the two endemic and painful health issues are progressive and the ONLY way to get some grip on these diseases is to wait on breeding and test; ideally also to retest parents dogs after 5 to know did they remain heart clear? SM clear? Knowing the health results as these dogs age is really far more important in many ways than those initial tests at say 2.5, though any dog being bred needs to be scanned, of course. But breeders miss out on perhaps their most valuable information by not rescanning when dogs are 5+. Statistically, 6 seems to be a good age based on this research and similar done on a cohort of 800 cavaliers.
On revealing the names of the early bitches: Davecav, there were important privacy considerations involved as well.
People gave pedigrees and scans for researchers to use on the basis of confidentiality. All the dogs named in the research were therefore identified only by letters. Nonetheless, there was much speculation on public forums by breeders claiming to have figured out all the dogs. Funny but some of the same breeders who demanded names of dogs and speculated publicly on dog identities have been the same who (utterly falsely) accused researchers of violating privacy by revealing dog names to others, something which was never done. Some of these people are unbelieveable: people with an obsession about discrediting researchers, who damned researchers for not revealing names, then have made false posts damning them for supposedly revealing names and scan results. Real bottom feeders, and they know who they are (the ones who continue to lie about the status of their own dogs, or let's just say, not be open about the truth). But I agree that the real damage has been done, as Margaret says, by the fact that so much is now understood with growing evidence to strongly back breeding approaches and still the same old, same old crowd ignore this and won't follow guidelines.
As others note too, was already way too late to try and breed away from the two early bitches; the lineages by even the 70s-80s permeated pretty much every pedigree and on top of that, many of the older lines that are known now to have likely been better in terms of SM, have also been diluted with 'popular sires' and known affected dogs, so the real need is to work to breed away from an already widespread problem and one that was widespread and worsening at the time of the original pedigree work...which by the way, would have been absolutely impossible without Bet's massive collection of thousands of painstakingly-collected pedigrees, which have been pivotal for both MVD and SM researchers -- breeders themselves failed to amass such a vital record! And for that all that care about cavaliers owe Bet a debt.