The date stamped in your I-94 card is determined by immigration laws that outline how long any category of nonimmigrant is allowed to stay. Students and some specialty workers are given a certificate of eligibility before they arrive in the United States. It is the date stamped on that certificate that will be transferred to the I-94 card. It is important to remember that it is the date on your I-94 card and not the expiration date of your visa that controls how long you can stay in the United States. Citizens of some countries can't get visas issued for the maximum period usually allowed by law.
Most visas permit multiple entries into the United States.
However, some visas allow only one visit. If you hold such a visa, you may use it to enter the United States only once. When you leave, you can't return again with that same visa, even if time still remains before its expiration date. Use this plain-English legal book to enter, live in and work in the U.S. temporarily or permanently. Includes all the forms you need to file with the INS and Labor Department.