No, it's either 7, which indicates a mini (ie: 10 shares per option instead of 100) or its the first number of the year. https://en.wikipedia.org/wiki/Option_symbol
Note that this is not taken into account in the other methods (they still usually work because the first option is not usually a mini). 

The other methods also assume that every option for each month has the same expiry date (it just checks the first one), which is not accurate - larger stocks have weekly's.