The SBGR001 evolved into the SBGR051 in 2010.
It changed over to a see-through back. (As you already know)
The crown got bigger, making it easier to use.
The date font was made thicker, making it easier to see.
The bottom of dial words (Japan 9Sxx-00X0) were made thicker.
The decorations on movement were also changed.
It also was given a 72 hour power reserve.
1. Switching over to an Automatic Winding System
The Magic Lever System has few parts, making it exceedingly durable. Winding up the 55 hour main spring was more than efficient.
Winding up the 72 hour main spring made me realize that the magic lever system has its limits.
It switched over to the reversing pawl wheels system (is this name right?), which has an efficient winder. The Reverse wheel was made more compact to increase efficiency, and treating the watch with hard coating increased durability.
The winding gears were rechecked, and were made more efficient by going back to using jewel bearings. That is why the number of jewels increased from 26J to 35J
2. Rethinking the Main Spring .
The length of the main spring (Spron510) was lengthened to 10 cm compared to the 9S55, it was widened by 0.5 mm, and it switched over to the 72 hour power reserve. (The main spring was thinned out by 0.2 mm to make it more compact).
The 9S55 spring is 40 cm long and 0.12 mm thick.
The 9S65 spring is 50 cm long and 0.10 mm thick.
1. Improving the Hairspring
The "Spron610" was used as materials for the hairspring. This doubled the shock resistance and tripled the anti-magnetization.
2. Improving the balance wheel
The balance wheel mortice was changed from 0.07 mm to 0.08 mm to increase durability.
3. Improving the gears
The gears were given a hard coat finish, and some gears were gold-plated with low abrasion resistance to aim for accuracy, making them more durable.