This tag is used for perennials to indicate there was only one planting date for the crop over a span of multiple years. For example, a grower plants alfalfa in 2005 and allows the crop to grow over the next 4 years with multiple harvest or mow events, but never replanted. COMET-Farm requires users to include a crop for every year in the baseline and any scenarios. ContinueFromPreviousYear indicates the crop is a perennial crop with a single plant date.
The same concept applies for users using the graphical user interface (what you see when you go to www.comet-farm.com).