Ah, I always just assumed from Ianto's bounciness in Sleeper that the date had taken place sometime between KKBB and Sleeper. In fact, I was quite into the relationship up to and including Meat, because it was so ambiguous and only really hinted at by bits of clever staging and scripting. It's just that on Jack's part it's stayed really ambiguous while Ianto's position has become more clear, and it's starting to look like Jack's taking advantage.