Is there a reliable source of Golden Dawn tarot material that's closer to its origins? (I seem to have misplaced Mathers' small booklet.) I have lots of commentary by later interpreters, bur nothing else I can point to as seminal. All the talk about the "Golden Dawn system" seems to lack a core body of knowledge that supports the premises.
Mathers 1888 booklet was published the year the Golden Dawn was formed. It does not contain the GD system. It is primarily a translation of Etteilla's meanings.
"Book T" is the seminal work! It is available for free on the internet from several sites, however all the copies I know of are missing Mathers' example readings.
The entire "Book T" (an Inner Order teaching paper), including the very helpful example readings, is available in Robert Wang's
An Introduction to the Golden Dawn Tarot - o.p., but it can easily be found used:
http://www.amazon.com/Introduction-Golden-Dawn-Tarot-Explanatory/dp/0877283702
And in Regardie's Complete Golden Dawn System (thanks Barleywine).
To truly understand the system, I recommend laying out Mathers' examples with a pips-only deck and following along, step-by-step. It's well worth the effort.
Free copies of "Book T" (lacking the example readings):
http://www.tarot.org.il/Library/Mathers/Book-T.html
http://www.hermetics.org/pdf/gd/t.pdf
from Benebell's own website:
https://benebellwen.files.wordpress...-felkin-golden-dawn-book-t-the-tarot-1888.pdf
from Abrac, an illustrated version - if you have Dropbox:
https://www.dropbox.com/s/9vfukh0vnvrj3cq/Book-T.pdf?dl=0
Greatly expanded material that stays close to the original in nature is
The Magical Tarot of the Golden Dawn by Pat & Chris Zalewski.
http://www.amazon.com/Magical-Tarot-Golden-Dawn-ebook/dp/B005C9X2QS/
Note: there are some complaints that he veres too far from GD tradition. I haven't read his book with a notion to compare details, so I can't speak to this.
There's a review of three books here: Wang, Zalewski and Cicero. Be aware that the Cicero's book contains magical work that's not from the original order but extrapolated from the GD system. I don't know if any contradictions exist as its been too long since I've looked at the book.
http://www.jwmt.org/v1n4/gdtarotbooks.html
Here is some additional Minor Arcana material that I typed straight from an original GD teaching paper, which I don't believe is generally known.
https://marygreer.wordpress.com/2008/03/04/the-golden-dawn-minor-arcana/
I have personally seen and handled several of the original GD notebooks (for instance - the paper transcribed on my blog above), and I have an original deck from the Felkins' New Zealand order. The Majors only can be seen here. I don't know why they never posted the Minors (a few of which can be seen on my blog post):
http://hermetic.com/gdlibrary/tarot/whare_ra/tarot1.html .
I believe the only contradictions you'll find before the 1970s or 80s (other than pictorially) are the few conceptual changes Crowley made to the Thoth deck. What happens after that is that many tarot authors start adding their own ideas into the mix without being absolutely clear that they are doing so. It's not always adequate to make a general statement that one is making some changes because readers often can't or won't make the effort to discriminate between that which is original and that which isn't, but will rather assume that there is no canonical work.
I'm not against people creating their own GD-influenced system but the two easily become confused - for instance everyone who says - "Oh, I use Elemental Dignities" - as if we should all understand what they mean and then, after much confusion, it emerges that what they do has only the vaguest resemblance to the original and no understanding of what the term "elemental dignities" actually means. This kind of thing can easily be the source of the idea that there's no true GD system.