A link is regarded as offline when:
a.) the linkorigin (URL where the link is published) does not exist anymore
b.) the link has been removed
c.) the linktarget has changed
Especially c.) very often creates confusion, because linkbird does not display this case explicitly. If the user then checks the linkorigin on the web a link is still targeting the domain of his project, but not anymore the original URL saved in linkbird. If the linktarget is then changed to the new URL, linkbird will mark the link as online again.
If only the linktext has changed, a small icon will appear in the column "Link text". A mouseover will then tell the orginal linktext and the current linktext published on the web.