Ok, to keep things interesting, here's something more speculative... some intriguing potential evidence that Sanders wrote under multiple aliases! If nothing else, it perhaps provides another road of investigation.
The excerpts below appear in Contributions to the Montana Historical Society, Volume 3. This was published in 1900, very shortly before EATCT. Sanders had left his post as Librarian for the Historical Society of Montana by this time. A letter from Sanders to the Society is included in this Volume that details some unfinished work that needed to be done. The Volume also included extended footnotes containing biographical sketches of two historical figures (Major John P. Bruce and Thomas Josiah Dimsdale) along with their actual writings. These sketches were attributed to a "Thomas Baker" from the Rocky Mountain Magazine.
A remarkable set of parallels with Sanders/Erdnase appear in these passages, suggesting that perhaps Sanders at one point also wrote under the name of "Thomas Baker." This is augmented by the high density of correspondences (given the brevity of the passages -- 130 and 140 lines respectively) and the fact that they all happen to appear in a published work from an organization that Sanders was recently and intimately involved with. It's also worth noting Sanders also wrote biographical sketches of his classmates in his college class reunion writings, so it was a form he seemed to enjoy.
The correspondences below include gambling references, unusual phrases, word choices, metaphors, anecdotes, topics of interest to Erdnase/Sanders, and even a biographical connection.
---- passion for play/gaming
Baker: PASSION FOR GAMING
Erdnase: PASSION FOR PLAY
---- bucking the tiger
Baker: in a hand at poker or BUCKING THE equally seductive "TIGER" (i. e.. playing FARO.)
Erdnase: We BUCKED THE TIGER voluntarily, and censure no one for the inevitable result.
Sanders: Make simple FARO, poker plays
---- dalliance with a deck/pasteboards
Baker: often found deep in DALLIANCE with the mystic pasteboards in a HAND AT POKER
Erdnase: DALLIANCE with the DECK is allowed [p60]
Erdnase: when the company will stand for DALLIANCE at all
Sanders: to tread the primrose paths of DALLIANCE and joyance.
---- cognomen [echoing Sanders' and Erdnase's interest with names and lexical derivations]
Baker: Major Bruce gained the popular APPELLATIVES of the "'war horse" and "wheel horse" of the republican and democratic parties respectively, COGNOMENS which will not die
Sanders: ERNEST JULIUS HYACINTH AMY...a name which served the double use of his COGNOMEN and our own mark of affection, for he was never known to us by his FRONT NAME or any of them.
---- many a...joke/prank/...
Baker: MANY A COVERT DIG was made and PRACTICAL PLEASANTRY PERPETRATED AT HIS EXPENSE... playing a JOKE upon him
Sanders: and enjoyed MANY A MERRY LARK and JEST and PRANK.
Note also the alliteration in both of these. And in particular the similarity between Baker's "practical pleasantry perpetrated at his expense" and Sanders' (elsewhere) "positive, probable, and possible" and "placed the passage presents a pleasing appearance." Erdnase also used similar alliteration in "passion for play," "pretensions of piety," "purified prodigals," and "presumptuous plebeians." Baker, himself, alliteravely titled his sketches with "Pencil Pictures of Pioneer Pencillers" (see below)
---- more (of a anecdote/letter/tale) "might be" said, but not here/now
Baker: a VOLUME MIGHT BE FILLED with ANECDOTES illustrative of his peculiar characteristics, but THESE MUST SUFFICE FOR THE PRESENT.
Sanders: More of the LETTER MIGHT BE GIVEN, BUT I REFRAIN.
Sanders whereby hangs a TALE which Sanders says is TOO LONG AND BOLD TO relate here
Erdnase: the back palm once helped us out of a difficult situation BUT THAT IS ANOTHER STORY.
--- pen/pencil pictures
Baker: PENCIL PICTURES of Pioneer Pencillers [title of Baker's Rocky Mountain Magazine biographical sketches]
Sanders: it would be in the possession of PEN PICTURES so graphic as to be of absorbing interest.
See link: https://scholarworks.umt.edu/cgi/viewco ... ontext=etd
--- parenthetical punctuation
Baker: and the paper's magnanimous (?) abstinence from unpleasant remarks about them brought ducats to the treasury and...
Erdnase: careless (?) dealer
Erdnase: when his error (?)
Sanders: innate and in(co)herent modesty
Sanders: We were fed fit for princes (?) stuffed with veal without the veal
--- unbiased (impartial | fair minded ) writer/engineer
Baker: reputation as an UNBIASED and IMPARTIAL POLITICAL WRITER.
Sanders: a perusal of the following excerpts from the text will convince any FAIR MINDED UNBIASED MINING ENGINEER
--- practice and proficiency in using a gun to hit a target
Baker: sallying forth to PRACTICE with the unwonted WEAPON; and how elated he was when he got PROFICIENT enough in HANDLING THE GUN to be able to HIT an oyster can at ten steps once in ten times!
Erdnase: PROFICIENCY in TARGET PRACTICE is not the sole qualification of the TRAP SHOOTER. Many experts with the GUN who can nonchalantly ring up the bull's eye in a SHOOTING GALLERY could not HIT the side of a barn in a duel.
---- characterization of young girls
Baker: and blushing like a SCHOOL GIRL when receiving praise
Erdnase: is to him much the same as a Saratoga trunk to a SUMMER GIRL
--- presenting/furnishing (with sequence of hyphenated adjs)
Baker: friends PRESENTED him with an IVORY-HANDLED, SILVER-MOUNTED pistol as a testimonial of appreciation of his work
Sanders: (the historian assumes that he is safe by a comfortable margin) in FURNISHING a CLOSE-FITTING, PLUSH-LINED, BURGLAR-PROOF biographical sketch
Sanders: a peculiarly fit subject for one of our patent NON-COLLAPSIBLE DOUBLE-RIVETED reinforced obituaries
We also find a biographical link
. Baker describes how Bruce died (in 1866) in the arms of his long-time friend Col W. F. Sanders, who just happened to our Sanders' father! And this information is conveyed in a very knowing way ("and it may be said"), as though the writer was intimately connected with the event (which Sanders would have been, as a boy living at home).
Baker: in his sickness, his long-tried and staunch friend, Col W. F. Sanders, was an almost constant attendant at the bedside, and it may be said that the departing journalist literally died in the arms of his friend.
These and other examples of correspondences between Baker and Sanders/Erdnase are given here (http://www.cs.columbia.edu/~coyne/erdna ... html#baker
Also of relevance is that Thomas Baker's name appears in the list of Honorary Members of the Society in an opening section of Volume 2 (which Sanders edited/published in 1896). So it's also possible that Baker was a real person who Sanders used as a conduit. One further avenue of research would be to see what else, if anything, was written/published by Thomas Baker and whether he was a real person or not.