Add paragraph about need for repeated Change Date updates

dosp-survey.ltx

@@ -654,6 +654,20 @@ evitaDB & always & 4th calendar year & Apache v2 \\
 
 \end{longtable}
 
+BUSL is notionally designed to apply to specific software \emph{releases},
+so that a Change Date applies to a particular version of a code base.
+That means that, for a project with an ongoing DOSP practice, BUSL is meant
+to be re-applied periodically with updated details.  The majority of projects
+we've seen have not yet demonstrated how they'll handle this process on
+an ongoing basis.  Most don't have a clearly-visible and systematic way to
+apply BUSL updates to ongoing development, although one project (Materialize)
+automatically updates its BUSL grant every day in order to keep the Change
+Date at a fixed point in the future.  For some projects, it is unclear at
+first glance exactly which version or versions of the code base the BUSL
+grant is meant to apply to.  The Change Date concept may be complicated by
+the fact that not all contemporary software projects have a reliable
+schedule of discrete ``release'' events.
+
 \subsubsection{Differences From Other Licensing Strategies}\label{differences}
 
 MariaDB describes some of the differences between BUSL and other