Like I said, it's not an exact science. Some petitions have issues and take much longer to adjudicate. Some get RFEs, have background check issues, criminal/arrest history, name hits in databases, eligibility issues, etc. It's not a straightforward, linear process. And some adjudicators are faster than others.
"Accurate" is relative as well. Yes, VJ processing projections come from user timelines, but again, is that official data? No, it isn't. It's reported data. Big difference.
If others are getting approved at 13 months, that's great. But until USCIS revises their processing time for that form, I'd plan on it taking closer to 16 months.