The Kodak records that I am familiar with give no dates, but merely show that Sheppard began the use of Sulfur as allyl thiourea to sensitize emulsions chemically. Later reports show use of Thiosulfate and then Thiosulfate with Gold. Agfa records show Thiocyanate as being used and then Thiocyanate + Gold. Both companies used a S + Au sensitization from before mid century, but it is unclear when the practice started as it is shrouded in "secrecy". One thing is clear and that is that both companies used these but with different compounds in play in the actual chemical reaction.

The use is usually 1 part of Gold to 3 parts of Sulfur. If you use Thiosulfate, then Thiocyanate can be added to accelerate the reaction or intensity the reaction. TAI (Tetra Aza Indene) can be used to restrain fog, but there are many publications listing alternate chemicals that inhibit excess fog growth.

Now, the above applies to AgBrI emulsions. It was not until the mid to late 70s that S+Au was applied to AgCl or AgClBr emulsions due to the excessive fog growth and lowering of contrast.

PE