in which year can we be assured the great horses of the past were not assisted by the use of 'excitements' that are now illegal?

​In 1666, at Worksop races, ‘exciting substances were prohibited’. So, it seems, as far back as the 1600-hundreds unscrupulous people were intent on gaining an unseen advantage.
In 1812, a stable boy was hung on Newmarket Heath for doping horses with arsenic.
In the 1890’s, the American-born Newmarket trainer Wishard was known for administering ‘substances’ to his horses, as were other English-based American trainers, which presupposes that in their homeland doping was not only a normal event but was also known about and ignored by the authorities.
In the 1900’s the use of cocaine was widespread in British horseracing, with the Hon. George Lambton publicly calling it a ‘scandal’. The use of cocaine as a stimulant caused horses to become wild and unmanageable, their eyes would be bulging and stare-stricken, sweat would pour as if they were composed of salt-water, with the effect lasting long after a race, and it was known for horses pumped up on cocaine to run headlong into walls and buildings.
George Lambton, weary of complaining about the situation to stewards of the Jockey Club, took it upon himself to prove to them that doping was rampant and had to be stopped. He informed the stewards that he intended to dope some of his own horses. Not his best horses but those he had long struggled to win a race with. He sent a horse that previously had good form but was now known as a rogue to Pontefract, had a friendly vet dope it, and not only did the horse win but the jockey could not pull it up until it became too exhausted to continue galloping. Lambton doped a further 5 horses which resulted in 4 wins and a second. The Jockey Club were finally convinced there was a problem only they could solve.
Indeed, without Lambton’s intervention it has to be asked how long into the future would doping been the scourge of the sport?
It was 1904 when doping was made illegal in this country, though in some places it is reported that it was a year earlier.
In 1912 saliva tests were introduced by the Jockey Club, testing for alkaloids such as theobromine, caffeine, morphine and strychnine. Yet rumours persisted that some trainers were gaining an advantage through doping and as late as 1933 it was claimed that 50% of horses were racing with such ‘excitements’ as cocaine, heroine and strychnine in their systems.
The aim of this piece is to pose the question, how can we be sure that the ‘great horses’ of the past, say before 1940, to take an arbitrary year, were not doped in some way? I make no claim against any trainer of classic or Ascot Gold Cup winners but in their autobiographies, they were hardly likely to admit to using banned or suspicious substances, were they? The top trainers were always under pressure to supply their rich and influential owners with not only classic winners but, as now, stallions for their studs. I suspect the temptation to gain any advantage, even if illegal, was tremendous.
It is why I don’t believe we can be 100% sure that any great horse of the era before 1900 was not being given one kind of ‘exciting substance’ or another. I am aware I am casting a dark shadow across the names of horses that appear in the pedigrees of most of the great horses of the post 2nd-World War era, horses that will include Eclipse, Ormonde, Pretty Polly and any classic winner you might mention during what might be termed ‘the doping era’ of British horse racing. 
During this dubious era, it was approaching a common occurrence on Newmarket Heath, as George Lambton described in his book ‘Men and Horses I Have Known’, for a wild-eyed, snorting beast of a racehorse to get loose and attack horse and man alike. Though it may be common in present times for horses to get loose on the Heath, I doubt if any of them attack another horse or any trainer on his or her hack to have to run for their lives.
I do not pretend to know the year when we can claim with any degree of certainty that dope or ‘exciting substances’ was not involved in the winning of any race in this country and would hope that the doping agencies in this country and around the world remain one-step ahead of the ‘dopers’. But we cannot be 100% certain, can we, as horses remain to this day to be found (innocently, perhaps) to have prohibited substances in their systems post-race? And, of course, with cctv at every racecourse stables, it is far more difficult these days to dope a horse to win, though to ruin the chances of a horse you only need to give it a bucket of water before a race.
The past is the past. The dirty deeds of unscrupulous people died, one would hope, with them. Yet when a breeder boasts that his stallion or mare has a blue-blood pedigree that extends as far back as one of the legendary horses of what we might refer to as ‘the dark ages of the sport’, he or she is, in effect, perhaps, championing the exploits of an owner or trainer who were simply superior in their use of illicit ‘excitements’ (not that they were illegal in their time) than their contemporaries?