Thanks for the response.
I was initially expecting any “was there; no longer there” routes to be in the extinguished table. But I guess the best course of action depends on whether these routes are really extinguished or have just been (accidentally) omitted from the latest PRoW snapshot.
If genuinely extinguished, then they should be removed from the parish tables and added to the extinguished table. If accidentally omitted, then they should be kept in the parish tables. But, of course, the difficulty is knowing which is actually the case as this requires searching out modification orders.
Could you perhaps keep the route in the parish table if currently mapped? Pro: it prevents unknown RoW numbers for mapped routes. Con: no longer highlights potentially extinguished routes and also means some inconsistency in how your tables work.
Or instead, how about a “potentially extinguished” table alongside the “unknown RoW” table, or even just a “potentially extinguished” flag in the “unknown RoW” table?