"Re: Breen's numbering problem: Dalton and Hamer had the same problem. That is why they used the obscure term "bis" when something came along that merited insertion. Open-ended numbering systems can be problematic as well. Richard Lobel has come up with a new and endlessly open system for numbering English coins but I find it cumbersome and oddly unsatisfying."

"I believe Mr. Schmidt's assessment of Breen's straight-through numbering system was perhaps a trifle harsh; first off, the empties are specifically "reserved for future issues" and are only available after currently circulating issues. No other meaning can possibly be intended. Should a new intra-type item be discovered (such as the cited 1914/13 Buffalo variety), it ought to be given the number 2592.1. If 23 new varieties of a particular coin were to be discovered the number of the last one would simply be XXXX.23. Sub-sub varieties (or die states) could be easily added, such as a XXXX.6.2. The obvious advantage is that the item number is always in order, and you can instantly tell when any item is a post-Breen discovery.

Secondly, the system allows for infinite expansion everywhere. No more large cents located within the Lincoln cents, which Breen, who was a superb mathematician, never intended. Also, given that the Federal issues are not strictly organized by denomination but by first by metal and then by denomination, (note nickel three-cent pieces occur before silver trimes), straight through numbering makes sense, since it is always easy to find any piece by number, regardless of type."