If you know you have to leave early then subconsciously you might be going for the number. Have you just rationalised later that it was for validation?

Staying till the end of the night would probably make a difference. I've only ever had a few SNLs but I had to work on them all night and stay until the end to close it. One interesting thing is one of the girls I had spoken to at the beginning of the night and was direct like you were. She blew me out but I saw her again near the end of the night and took her home.

The next day I asked her if she remembered speaking to me at the beginning of the night and she said no. In fact she was adamant that the first time she'd spoken to me was at the end of the night. It might have just been the drink making her forget (but more likely it was her slut shield activating as on the first interaction I had asked her to come back to my place).

But I wonder if my first direct approach made an impression on her that triggered something when she saw me later on in a different pub (when she approached me). If you can find out where they're headed later on it's worth going there...and stay until the end.