Congratulations Twins 1940-S Mercury Dimes With Twin Mint Errors.

Here are two more in this series that are very similar. Notice the foreign chunk next to the initials is still there but is fading. Also to the NW of "IN" there is a bunch of die scratches and another big hunk of foreign material that also fades out through the series.These dimes are coming out of a set of 220 dimes I bought at an auction. I believe they are die change series showing the difference after making changes to the dies. Maybe collected by a mint employee back in the day of minting. I have others in series before and after major Double die incidents, like 1939-P, and 1939-D the 1942-P and also Roosevelts of the early series. Let me know if they interest you and or if you can recommend someone to attribute these. I truly believe I have a rather unique and special collection.
regards
Paul

Here's an image of my stage B FS-901.
Here's an obverse die that looks like the die crack in your second post.

My impression of your first images, "twins" is the curled line under the 9 is a clash artifact and the mark near the designer initials being on both examples must be as well. My stage B examples do not have these as a mint worker must have polished the heck out of the die to remove the clash marks and the die crack leaving the gouges at the bottom of the bust. From what I can tell from all the examples I have from 1940-S is they didn't have enough dies to produce what they needed to and really stretched the die life.

My photog set-up is this, a Canon body mounted on a bellows using various enlarging lenses