The best LD50 story I've heard was an Agriculture Canada scientist working on biocontrols for pests (think natural pathogenic organisms like fungi or bacteria to control weeds instead of chemical pesticide). Policy and commercialization required an LD50 for a bacterium they were working with. It is nontoxic; the lab calculated the volume of bacterial solution at commercial application strength that it would take for a rat to drown (but obviously did not harm any animals). Sometimes regulatory compliance needs creativity.

Unfortunate that not all labs are able to work similarly, especially as you say for doses where we already know harmful levels and LD50 is a bureaucratic requirement or an easy paper.