Wow -these pics show very visible differences. I have an L stamp TC B40 that is thicker than my later TC B35s - I think it may be what was said above- to make up for weight/structure of the 40. It would be interesting if it was done for some other reason. Not sure how to account for the difference between the straps if those are Birkins of the same size -regardless, they should certainly be "holding up". You would think that in a globalized world culture were "athleisure" is being sold, that making bags lighter and thinner to appease customers would never cause H to shirk their culture/responsibility of creating high-quality bags similar to what Grace Kelly or Jane Birkin first carried. On the other hand, a friend suggested that having to destroy a major amount of R year bags may have had its costs. Who knows?
H, while classic, has changed over the years in terms of leathers and production. However, I have to believe that fundamentally, they would try to avoid putting out poor product that would weaken or cheapen the brand. Given the investment we have all made, I hope that's the case.