Visa Bulletin is a statistical projection based upon rules of statistics as well the law. There are laws as to how many visas you can allocate each trimester or quarter. There are many things to be considered in a visa bulletin. Hence visa bulletin is merely a projection. It is not accurate. Normally you will use the dates for filing visa application chart, but USCIS will indicate on that page that sometimes you can use application final action dates.
The way it works is let's say your date is current in December. Visa bulletin gets published 15 days into the month, so by November 10 to 15 you have got your dates for the next month. Remember your adjustment of status applications should not get there before December 1st. You have all of the month of November to file your application. Dates remain current for the whole month.
Regarding your question normally you will file according to the visa bulletin dates unless the USCIS website shows that the final action dates are different and those are the dates you can use.