The term registered players only came up since 1968, when amateurs like Ashe and registered players like Okker wer separated from the contract pros. Ashe could not take the prize money at Forest Hills in 1968, while Okker could. Krishnans offer, which is reminded only by the living memory of Krishnan himself, was over 3 years, while Hoads and Lavers offers were over 2 years. Krishnan names as reasons, why he turned it down, the possiblity of playing at Wim and Davis Cup. To turn pro had the consequence, to get out of the limelight at the big stages. The amateurs had the big stages with greater publicity, coverage and public attendance. They were hosted and pampered by rich club officials, and had many prominent friends among film stars and politicians. If someone is interested in the great time and high life of amateur tennis, he should read Gordon Forbes book.
The pros had to go to second rate clubs and sports halls. Nobody cared, newspapers and tv had coverage only, when they played Wembley or New York. Some top amateurs could make a good living out of the am tour, like Patty, Drobny, Larsen, Flam or some Aussies, nobody denies that. Laver made some 12000-15000 $ in his Grand Slam year 1962, when he played some 35 tournaments, winning 22. Newcombe the top amateur made 15000$ in 1967. Emmo and Santana played some 25 events overall per year, say at the highest 15 events, where they could get 1000-1500$ appearance money, due to the 7 months rule. Maybe they were in the range of medium pros like Buchholz or Segura, but the top pros like Laver or Rosewall certainly made more money. And at least for their cigarette contracts, the amateurs had to play taxes, too, other than that would be illegal. They were not Al Capone.