Correct, developers would need to submit to Nvidia enough "screenies" for the training, and training can get accuracy over time. DLSS updates are handled by Geforce Experience. The training is free since they made a commitment and likely to remain free since no vendor charges for Driver updates (game optimizations handled by IHV developers). When it first appeared some publishers did mention they would apply DLSS to some of their old titles since it's fairly quick to implement in game code. Just a matter of internal schedules.