See "21. Investors don't like to say no." in http://paulgraham.com/guidetoinvestors.html

Investors often feel the need to give a made-up reason, but the real reason is that they're not as excited about you as about something else. Don't be discouraged -- even the most successful companies got many nos on the way to their first yes. Don't change your business strategy based on the reason any one investor gives you, although if several good investors give you the same reason, you might want to think about it.

BTW, it's normal to extrapolate retention to a yearly number using cohort analysis. Your claim is a bit like "I can't have been going 80 MPH because I've only been driving for 30 minutes!"