A documentation set may need to be re-linked whenever any file in any of its documents changes, or when any document is added or removed, or moved to a new location. The HTX linker detects changed documents by observing the modification dates of the document ".htx" directories, the associated index files, and both the modification date and contents of the "htx.log" date-stamp file in each document library.
This process is effective, except that it is sometimes possible to modify an HTML file within a document without changing the modification date on the ".htx" directory that contains it. This is particularly likely if the HTML file resides in a sub-directory within the document. If such modifications are carried out, a simple remedy is to use the UNIX touch command to update the document's ".htx" directory and record the change before running the linker.
As an alternative, the hlink command may be invoked with the -d flag to specify a deep dependency test of all document files. This causes it to check the modification dates of all the HTML files in all the documents in order to detect changes. This is a thorough way of detecting changes, but may be rather too slow for regular use on large document collections.
You should also remember that re-linking can be rendered necessary not only by changes in document contents, but also by changes in document location. Thus, if documents or libraries are moved, it is always wise to re-run hlink.