Forms I-151 are no longer issued, however previously issued I-151's are still valid.
Form I-551's verifies the person is lawfully admitted for permanent residence. An alien who is lawfully admitted for permanent residence meets the qualified alien criteria however he/she must still pass the eligible alien criteria (identified under Sections 3231 and 3232).
Aliens who marry a US citizen receive an I-551 with a 2 year expiration date. If the alien is still married to the US citizen at the end of the 2 year period, they are given indefinite permanent alien status. The alien is considered a qualified alien and eligible to receive Food Stamp benefits during the 2 year period if he/she passes the eligible alien criteria (identified under Sections 3231 and 3232).
South Dakota Food Stamp Certification Manual • Revised April 2003