I recently got my hands on new and old Osram NAV-E/I self starting 50w HPS bulbs. It looked like there were two glowbottle starters in the older bulb and only one in the newer bulb so I decided to sacrifice (I am so sorry, it felt bad) two of the different generations of bulbs to study their internals. What could be the reason for there being two starters in the older one and only one in the newer one? Cost saving or something else?

The second glow bottle, isn't a starter, but a thermal disconnector, that disconnect the starter when the lamp is hot.