When is a party not a party?

One of my tendencies that people who know me- whether personally or through reading this blog- might recognize is that I often have difficulty putting times, such as dates, months or even years, to a lot of events that I otherwise remember quite well.  For example, some time back before I met my wife, a female co-worker (yes, that's one of the reasons I wanted to emphasize the above) asked me if I wanted to go to a party she was having at her house, if I remember correctly, that night.  Since I didn't have plans for whatever night it was (or pretty much any other night, come to think of it), I agreed after making arrangements for her to pick me up at my apartment as I don't drive and it was quite a distance away.  After work ended that day, I went to pick up some juice just in case the refreshments weren't to my liking (while I don't have anything against drinking per se, it's something I have never developed a taste for personally) and then home to change.  She arrives later on and we drive over to her house.  After awhile there, though, it appears that no one else is going to show up and eventually she takes me back to my place.  I think nothing of it until....