Isn't that done in the application process? Assuming the applications are read and prepared carefully?
Really? They're calling you in for an interview and they don't have your application in front of them and haven't refreshed their memory? YC gets results, so I guess if it works it works, but I find it surprising that the assumption is they're going to be unprepared like that?
I think whether or not they 'remember' the nitty gritty details of the app during the interview is irrelevant.
You need to sell them on your vision and team during the interview. You should be able to do this within 5 minutes whether or not they have the foggiest idea of what you are doing.