I always wonder about that...
When we pull two of the same bottle out and they're around 100 years old and late-blown or early machine-made, we see a lot of differences between the two depending on where the bubbles in the glass ended up or how the colour differs slightly or how messy the tooling is, etc.. But, when people 100 years from now pull out a 1950s ketchup, yeah they're gonna be like, "oh my gosh, this thing is 150 years old!" but when they pull out another and it's the same ketchup bottle, it will look virtually identical to the first. No bubbles, no colour, no fun stuff.
What I'm saying is that even though I tell myself I'm a good person for leaving those ketchups for future diggers, I think those future diggers are still gonna hate digging 1950s ketchups! Haha! So next time you're reburying those ketchups, take the opportunity to work on your evil grin!