A bill may go through many stages on its way to becoming law. It is important to look at the original version of a bill and any amendments, proposed or adopted, when compiling a legislative history. Sometimes the original bill will have a preamble or statement of intent that doesn't appear in the final version.
For more about bills, see the Guide below from the Office of Legislative Services.
It's unusual to refer to a New Hampshire law using the bill number though it does happen occasionally (SB 2 is an example). The bill number makes it easier to find relevant pages in the legislative journals because modern legislative journals have a bill number index (called the numerical index) with journal page references. A bill's number stays the same throughout the legislative biennium so a House bill will always be "HB" even when it moves over to the Senate and vice versa.
To find a bill number: