Contract Bridge wasn’t even invented in 1912. At that time, they would have been playing Auction Bridge (or possibly Whist). What’s relevant for this discussion in Auction Bridge is that the holder of all 13 diamonds would get score grand slam regardless of how few diamonds s/he bid to win the auction. So s/he could simply keep bidding one level higher in diamonds over any other bid and not have to worry about partner passing before 5 diamonds (game) or 6 or 7 diamonds (small or grand slam) was actually bid.