I'm in agreement with you on this however I should porbably have noted that the vast majority of my work is for rail cars from the 50's and early 60's. This is the era most often modeled by my friends and myself. Ergo a lot of it is from the 40's and can go back as far as the 20's.
In today's world, and going back to the 70's, 60's and 50's, depending on the road, methods changed.
That said I still maintain that the best way to draw accurate artwork is to work off [photos of the prototype.
Of course to get the correct dimensional data one needs some very good photos and the era I usually model has a decided dearth of some photos. For modern stuff someone with a digital camera, even phone camera, can go get proper photos. And for really old stuff it may be possible to find photos from old glass-plate cameras and they can often be enlarged to show all detail very well.
But for all the photography starting with the invasion of Japanese SLR's on the 50's and 60's, the resolution just isn't there unless tee photographer was specifically trying to record the data.
BTW, even with stencil's the lettering can vary. Maybe not the individual letters but find some photos of used cars acquired by the CNW in the 70's and look at the reporting marks. Perfect alignment was not one of their requirements.