For the past 25 years we have been following the IPC standard starting with the IPC-SM-782 land pattern standard.
Here is a chart from the IPC-SM-782A for the Chip Components -
The name 2012 is based from the "Nominal" component dimensions - 2.0 mm X 1.2 mm.
However, the nominal component dimension for the 2012 "width" is 1.25 mm.
In the mathematical world of rounding, 1 - 4 round down and 5 - 9 round up.
So 1.25 mm rounds up to 1.3 mm for the accurate consistant name.
This mathematical automation correction of land pattern names was finally updated in the LP Wizard when we released the first Mentor Graphics version of the tool. Fortunately it only affected the 2012 (EIA 0805) component for Chip, MELF and Molded component families. This was a long overdue upgrade that now produces a consistant reliable land pattern name because the mathematical rounding for automatically generating the land pattern name has finally been corrected after 25 years.
So the answer to your question is: If your component nominal length is 2.0 mm and the nominal width is 1.25 mm the land pattern name should be 2013.