Just For Fun Discussion - Three Lincoln Wheat Cent Puzzles

I thought it might be fun just to throw out two variety and one error head scratchers in the Lincoln Wheat cent series as a "just for fun" discussion, if that's OK with the moderators.

Puzzle #1 - Lack of 1926-D and 1926-S RPMs. There are quite a few remarkably bad punching jobs for 1925-D, 1925-S, and 1927-D cents. How in the world did 1926 escape the RPMs? It isn't that the mint did an awesome job with mm placement in 1926, since some mms range from aligned directly under the 9 to aligned slightly east of directly under the 2. How did they manage to get clearly punched mms for this year?

Puzzle #2 - San Francisco retained cuds. There are highly disproportionate numbers of identified Retained Cuds for San Francisco cents, especially in the 1940s. Why? What did San Francisco do that Denver and Philadelphia did not do to break dies?

Puzzle #3 - What were they thinking (or maybe drinking) when they punched mint marks in 1956? The 1956-D cents have some of the most bizarre mm varieties in the entire Lincoln Wheat cent series. There are at least two D&D varieties, D&D NW (over the tail of the 9) and D&D way South. There are the two disputed D/S and D&S far West varieties. The wide punches are so far off that they defy logic.

I'd love to hear the best stabs at explanations for these!