Hi foundinrolls ........ your post is a really good educational one for the error folks that are new to the hobby . I want to mention that this die wear is about like coins that are found after being in circulation for a while. on the heavily circulated coins the extra lines of the doubled die coins usually wear down almost like the worn die coins.
Yep, circulation wear is another factor. if the coins surfaces wear down to where the grooves are no longer visible, you can still use the "footprint" of the lettering, for example to ID the die variety.