@Janealogy @Wuzzy
I'm not sure what crofts are (farms? piece of land?), and how they can be mapped (as a point or an area?), but for things already gone, there is a specific project called OpenHistoryMap.
As for details, almost everything can be mapped (benches, trees, bins..) so I see no limitation
@Janealogy @Wuzzy
An example of detailled mapping in Scotland: at the max zoom level, even walls and barriers between fields have been mapped. https://www.openstreetmap.org/#map=17/58.49035/-6.24027