Not a chart. A table. But you do know how tables are developed, don’t you? People go out and make measurements and do calculations and make more measurements. Wire rope stretch is a known, studied, and well defined phenomena. And that not just by bicyclists. The article and calculator I linked to are not about bicycle cables. It applies to any wire rope.

As for “physical proof”, I’ll refer you all the bikes that need cable adjustments after installation of a new cable. And, no, I’m not talking about cable housing. Put a new inner cable in old housing and the cable will need adjustment for cable stretch in relatively few miles and then won’t need it again. Almost like there’s an initial stretch followed by a long time of being stable.