The following was obtained from an attorney's web site regarding the No. of times a re-entry permit may be obtained in general:
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The form, I-131, referred to as the "Application for Travel Document," has to be filed while the person is in the U.S. The maximum period of time for which a reentry permit can be issued is two years from the date of issuance. Generally, a reentry permit can be issued twice, each time for two years, totaling a period of four years. After that, any additional requests for the reentry document are discretionary on the part of INS and are often denied. Each member of a family has to file a separate application and filing fee to the INS in order to obtain a reentry permit.
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Is it true? What if the permit was applied but each time, only short trips (e.g. less than 6 months) took place instead? Can someone apply for the permit several times just to have more peach in mind in case if a lengthy trip (>1 yr<2 yrs) will be needed in future?