Regarding the rosette on your Alvarez... that used to be the mark of a fine Spanish guitar. As you pointed out, tiny little pieces of marquetry arranged like a symmetrical mosaic. There are a few makers that still do this.
On my little guitar, CS is the designation for Custom Shop. GE is for Golden Era, which is their line of vintage reproduction guitars. They also have a top-shelf line dubbed Authentic Series which are made as direct copies from scans of source guitars in the company museum. As I understand it, they are 100% handmade, not pulled off the production line and finished by the Custom Shop.
Martin is nothing if not organized. Most of their styles and models (as written by Longworth and Johnston) were clearly defined by the late 1800's, the famous X-brace having been perfected by the mid-1850's. The next big evolution of guitars really began in 1929 when a (plectrum) banjo player named Perry Bechtel suggested they build a guitar with a longer scale, and more frets accessible. Martin responded by altering their 000 body, making the body wider at each bout, but shorter/squatter in length, producing their first guitar with 14 frets clear of the body, and a solid faced headstock. (as opposed to the slotted headstock which was the standard of the time) This also changed the location of the X-bracing on the soundboard, altering the responsiveness to a more focused sound. The resulting guitar was called Orchestra Model or OM. The OM designation only lasted until late 1933/early 1934, and was re-branded 000. Simultaneously, in 1931 the Dreadnought guitar was developed from an old pattern used to make Hawaiin guitars for another company. (Oliver Ditson) In 1934, the Dreadnought simultaneously evolved from a 12-fret to a 14 fret body, and became what we now recognize as a regular guitar. All their models followed suit in the coming years, each getting the new 14 fret re-design. Though the 12-fret pattern never went away, it faded to somewhat obscurity until the 1960's... something about a folk boom, or so I read. =)
Obviously, that's the short version of how/when/why the Martin body shapes changed.
My little 12-fret Custom 00 is a throwback to a brilliant, very transitional time. I designed it very much with the same mindset as when I was deciding how to do my Custom Alembic.
