My girlfriend from Mexico has a B1/B2 visa. Using this she has transited through the united states on several occasions in the past year. This time, when she entered, the JFK officer did not stamp her passport. Instead he stamped the I-94 form with her entry date using the admitted stamp and wrote in pen, another date six months in advance. Usually she is issued a 6 month visa upon arrival. This seems to be a six month visa, but we don't understand why he did not stamp the passport itself and are concerned that there will be problem upon exit or future reentry. Any ideas?