This is much more crucial than a frame holding a speaker. I'd be much more worried about how my speaker was made and the effect it has on my tone than whether or not the frame holding my speaker was going to corrode after 200 years instead of 210 (random numbers). I knew I shouldn't have left my cab in the back of my space cruiser! Maybe we should analyze the ink on the stamps next. I hear that Marshall's Celestions use a low grade ink made in Indonesia when stamping serial numbers on the frame as opposed to Mesa that uses ink from a US factory in Nashville. I don't want no stinking Indonesian ink on my frame...
My point is who cares if it sounds good and gives you the tone you want? We should worry more about playing guitar and making music than whether or not our speaker frame can last 210 years instead of 200. If it sounds good, that's all that matters. You're not going to have any reliability issues with any frame that Celestion ships in your lifetime, your kid lifetime, you grandkids, lifetime, etc.