There is a difference between a used/unused list and a reserved/available list. In the old string id topic, both types of lists were in there to some extent. Although a number of people did not have problems understanding the difference, there was also a number of people that were confused. Anyone designing buildings does not need to know anything except what is the next available block. So the current approach is simply that: show the next few available blocks. The blocks that have been reserved are still shown. But to reduce the confusion further, the reservations in the current range is in a separate topic than those that were in the previous range. There is still a list that contains what has been used, including those used by Blue Fang. This list has two purposes. One is to know what range to use next once the current range is completely reserved. The other is for possible reuse of messages, in order to minimize how fast ids are used up. However, there are situations where a message cannot be reused, even if it looks like it is exactly the same. At some point those messages should be separated out so people will know which messages can safely be reused, and under what circumstances.
Even though building design is not occurring at the rate it once was, it is still occurring.