Technically, every record should have a net code. Banders sometimes leave it blank anyway. Starting in 2006, IBP has asked the banders to code “?” in this field if the net is unknown.
The output format allows for up to four-character net codes, but the standard MAPS data sheet has only two columns.
Starting with the 2006 MAWS season, some locations set up a reference grid so that they could record the location of color-banded birds that were observed but not captured. Grid coordinates are expressed as one or two letters followed by one or two digits. Examples: N6; BB12.