census building permit analysis

[Jason Malabute]

So I finished my initial market analysis. One of the factors that I looked at was the building permits issued in 2017 for each MSA. My question is why doesn't the annual issued for 2017 equal the total amount if you add up all 12 months for 2017?

For example, if you look at Houston, The Woodlands Sugarland Texas the total building permits issued based on annual report was 42673, but if you add up all 12 months from the monthly report the total was 44879.

Please note that I used the monthly/annual  reports titled  "New Privately Owned Housing Units Authorized Unadjusted Units by Metropolitan Area"  which I got from https://www.census.gov/construction/bps/

I just want to make sure my analysis is accurate. Thanks!