I’m presuming the bottom one to be the newer model?

Ignoring arc tube construction the orange etch of the lower one and the UV glow bottle makes me think it is the newer one too. Wasn't the trend normally to switch away from multiple piece arc tubes and into more power ball type arc tubes like the top one?

Seconded (Thirded) the bottom is the new. The upper one has the frame bending and hexagonal clip on the dimple all familiar from Tungsram lamps. The bottom one uses something simplified just to fit. so would be made either on new machinery or in a new factory location

That was the trend when there was effort put in place to improve HID, so up to about 2013 thereabouts. Nowadays the trend is to shift production to the remaining factories, regardless of whether their technology really has all the same advancements made in the original plant. Not saying the new lamp is bad, it might work just as well

Interesting, but why would they go from a single moulded arc tube to the 3 piece one?, unless they had surplus ones in the factory?

@James said that the older arctube is more opaque than the newer arctube.

The 3 piece arctube on the newer made one would have a higher output since Dor said it is more transparent than the old 'powerball' style one

The first GE high wattage CMH lamps had to use Japanese made slip cast single piece arc tubes because they had real problems making such a large bore "traditional" burner that wouldn't shatter under the stress. Even the slip casting method was hard to do and it was very expensive (the raw ceramic cost about as much as the production cost of a complete 400w lamp!) Later on though the problems with managing stress in the structure was overcome which allowed them to switch to a cheaper alternative that they could make themselves.