SO - Spill Over
From Immigration Wiki
Spill Over of visas first SPILL ACROSS (FALL ACROSS) and then SPILL DOWN (FALL DOWN).
Fall Across/Spill Across: It is a horizontal reallocation of visas within a category. (eg: eb3 row gets first preference of unused numbers from eb2 before eb3 India or China or Mexico...) If an oversubscribed country demands relatively small quantity of visas in the family preferences, the excess visa numbers would be made available to the Employment preferences, as long as the total number use is still within the annual limit for that country. In such case, EB1, EB2 and EB3 would each receive 28.6% of the excess numbers, and EB4 and EB5 would get 7.1% each.
Fall-across may also happen if an oversubscribed country lacks demand in the employment preferences, which would result in excess visa numbers being allocated to family preferences.
Sometimes fall-across can prevent a country from becoming oversubscribed. For example, if a foreign state has very little demand for FB visas, but significantly more for EB visa numbers, the allocation of unused visa numbers may exceed the limit established for employment categories. However, as long as total demand is still below the 7% cap, this country would not be classified as oversubscribed.
Fall Down: It is the vertical reallocation of visas between categories (eg: unused numbers from eb1 go to eb2....) Unused visa numbers in a higher preference level can "fall-down" to lower preference categories. For example, excess EB1 numbers can "fall-down" to EB2. Similarly, EB3 will receive numbers not required by EB1 and EB2.
Fall Up: This mainly happens within the Family or Employment based category Unused visa numbers in EB4 and EB5 can "fall-up" to EB1.
DOS explanation of the number distribution between Family and Employment based category: http://www.travel.state.gov/visa/bulletin/bulletin_4747.html
- If a foreign state other than an oversubscribed country has little Family preference demand but considerable Employment preference demand, the otherwise unused Family numbers fall across to Employment (and vice versa) for purposes of that foreign state’s annual numerical limit.
- For example, in FY-2009 South Korea used a grand total of 15,899 Family and Employment preference numbers, of which 1,688 were Family numbers and 14,211 were Employment numbers.
- This grand total was well within the FY-2009 per-country numerical limit of 25,620 Family and Employment numbers combined, so South Korea was not oversubscribed.
- The unused Family numbers were distributed within the Employment categories, allowing South Korea to be considerably over the 9,800 Employment limit which would have been in effect had it been an oversubscribed country.
Spillover before 2009: (incorrect interpretation according to USCIS)
Unused EB1 visas was shared between EB2 and EB3
Unused EB1 => EB2 ROW => EB2 retrogressed
Unused EB1 => EB3 ROW => EB3 retrogressed
Spillover after 2009 - changed to the correct interpretation according to USCIS:
Unused EB1 => EB2 ROW => EB2 Retrogressed => EB3 ROW => EB3 Retrogressed.