2nd Generation Changes (2006)
In 2006, Selmer changed the thickness of the metal used for the tenon on the bottom of the Reference 54 alto sax neck. They went from using a gauge of .75mm down to .55mm thick. Since the outer diameter of the neck stayed the same, this switch actually increased the bore through the tenon of the neck by .40mm (.20 on each side). In terms of acoustics, this is a rather noticeable difference. The result is that the horn played a bit bigger and responded easier than before, especially in the lower range of the sax

3rd Generation Changes
This change was primarily in the octave mechanism. The neck tube and the tenon thickness stayed the same as the design changes from 2006. The 3rd Generation neck brings in the octave key and mounting bracket implemented in the 2010 “Jubilee” release of the Serie II & III saxophones. The octave key itself has been reshaped to look more elegant and uses a slight revision to the appearance of the classic Selmer “S” logo on the neck. This series also saw the design of the octave key’s mounting bracket completely changed. The new design is one that gives much better stability to the octave key and also is a smaller overall footprint. This lighter mechanism decreases the weight of the neck and allows for better vibration and response from the neck tube itself as the overall weight of the neck was decreased by 7%.

The tenon mounting design was also improved. The new design guarantees a better fit of the tenon on to the neck tube and eliminates some of the imperfections that can be caused to the bottom of the neck tube inside the tenon. This change was more of a manufacturing quality improvement rather than a performance change.

Reference 54 Alto Sax Neck Change #2 – Octave Key Mounting Design
They also changed the mounting mechanism design on the Jubilee models that results in a much more stable and secure fitting octave key. The old design had the thicker brass of the key folded over the mounting bracket. This made it very difficult to fit the key tightly and allowed noticeable side to side movement in the key fit. The new design features fixed mounting posts underneath the key itself. This allows for much great fitting control at the point of manufacture.

Reference 54 Alto Sax Neck Change #3 – Octave Key Guide
Selmer actually put this change in to place a few years before the Jubilee. They used to install a “guide” near the octave pip. This guide served very little purpose and added weight to the neck that dampened vibration. So on the Jubilee models (and a few years before), Selmer removed this guide entirely.