The U.S. Congress sets an annual limit to the amount of green cards that be can issued. For EB-3 Unskilled, no more than 10,000 visas can be issued throughout the fiscal year (October 1st to September 30th). The Visa Bulletin is published by the United States Department of State (DOS) to manage that number and ensure they are able to issue visas throughout the year. On a monthly basis, DOS determines how any applicants they are projected to have that month and compare that number based on how many applications they have already received for the year and estimate how many more they believe they will receive for the rest of the year. Bottom line: If they project the number to be over what will be available for the year, they will attempt to slow down or freeze the filings by moving the priority date to match what they believe demand will be.
The priority date is the date your labor certification is received by the U.S. Department of Labor. It represents your spot in line.
All of the dates you see on the Visa Bulletin tables are called “cut-off dates”, which correspond to the beginning of the wait line. You should always check if your priority date is before the cut-off date. It represents the date by which USCIS or Consular officers are currently issuing visas.
The Visa Control of Reporting Division of DOS is responsible for determining the movement of the “cut off date” each month and for releasing the monthly visa bulletin.
In October 2015, DOS introduced the two-chart system. One chart is designated as the Final Action Chart which is to represent the date when a green card or immigrant visa may be approved. In plain terms, it represents who is at the front of the line to be issued a Green Card and the priority date of the cases which are being reviewed and issued by USCIS or Consular. For example, if the “cut-off” date is January 2017, then they are reviewing cases with that date as their priority date. The second chart, date for filing, was designed to be primarily for consular processing cases. It is supposed to be the date when the immigrant visa applicants should be notified by the National Visa Center to assemble and submit their required documentation. Both dates are determined by DOS on a monthly basis based on the number of immigrant visa applications they received for the month, their processing capabilities, how fast they can review the case, and several other factors.
Each month, USCIS does its own formula based on both charts. Once DOS releases both charts to the general public, USCIS will look at both charts, look at its own processing capabilities, the number of officers they have available to process cases, and other factors to determine whether they want to use Chart A or Chart B. If USCIS determines that they have more immigrant visas available than they will have applicants, they will go with Chart B. If they seem to have more applicants than immigrant visas, they will slow it down and go with Chart A. They let you know here: https://www.uscis.gov/visabulletininfo. As a general rule, they are supposed go with Chart A, but oftentimes, their own formula shows they have room for additional I-485 filings and they go with Chart B.
If My Case Is Current in Chart B and USCIS decides to go with Chart B, Does That Mean My Green Card Can be Approved Too?
No. While USCIS may let you file a I-485 based on Chart B, they cannot approve a I-485, however, unless and until the cutoff date in Chart A moves past the priority date for that case.