We keep mentioning how transspecies as a term has existed long before the radqueer & transID communities formed, and started claiming it as part of those communities despite it's actual usage within nonhuman/fictional/unusual human species identifying spaces and objections from said spaces.
As a sort of quick thing to back this up, here are some examples before the year of 2020 (estimated beginnings of the radqueer/transID community)!
All of this excludes troll posting/mockery, and is focused on NH/FICT community's discussions. Some additional content warnings are provided for some of the e-mails, however.
This is not extensive, feel free to show us any other finds (excluding alt.horror.werewolves e-mails, we've already scoured trough everything. There is actually more mentions via that, but all from the same person).
01 - "Gender-bender" e-mail, 1999. Included in this section due to the unclearness of if the original author of the e-mail identifies as otherkin or transspecies personally.
[Link] [Link 2] [Archive] [Archive 2]
02 - "On cosmic surgery and personal identity" e-mail, 2005
[Link] [Archive] [Archive 2]
03 - "Da Jakkal's work revisited" e-mail, 1999. Warning: has some outdated terminology/beliefs.
[Link] [Archive] [Archive 2]
04 - "Re: Introduction" e-mail, 2002
05 - "Re: Shifters: in need of Help." e-mail, 1999. Warning: thread has mentions of an un-nameable native American creature.
[Link] [Archive] [Archive 2]
06 - "Re: Musing of the Week" e-mail, 1999
[Link] [Archive] [Archive 2]
06 - "Re: define were" e-mail, 1997. Warning: thread has mentions of an un-nameable native American creature. (This is the second time we've have to issue this CW. Sucks.)
[Link] [Archive] [Archive 2]
07 - "Re: Fun with Faith" e-mail, 1997. Same warning as above, unfourtunately.
[Link] [Archive] [Archive 2]
08 - "Re: Questions on Were's/Shifting/etc" e-mail 1997. Same warning, a lot of early instances of the word being used seem to all be from this one being, sorry.
[Link] [Archive] [Archive 2]
09 - "Re: Slithering into AHWW" e-mail, 1997
[Link] [Archive] [Archive 2]
10 - "Re: Odd Dreams" e-mail, 1998
[Link] [Archive] [Archive 2]
11 - "Shifters: WereBreeds" e-mail, 1999. Warning: has some outdated terminology.
[Link] [Archive] [Archive 2]
12 - "On the appropriation of trans narratives by therianthropes" article, 2013. Contrary to the title, it is supportive. It does mention the native creature again due to excerpting an AHWW member's ramblings, so thread with caution.
[Link] [Archive] [Archive 2]
13 - "An Introduction to Animality" article, 2009
[Link] [Archive] [Archive 2]
Usage of term for clear self identification (flags and symbols are included):
01 - "Re: A question to everyone out there" e-mail, 1997. Warning once again for mentions of an un-nameable native American creature, and questionable identity that may or may not be considered cultural appropriation (we have no place to say as we are not native). Still, it is an clear account of identification with the label and experiences that'd come to be associated with it.
[Link] [Archive] [Archive 2]
02 - "Chewing and biting (and intro)" e-mail, 1999. The poster at the time of posting already specifies that they do not identify with the label anymore, but used to.
[Link] [Archive] [Archive 2]
03 - "Transspecies Pride stamp" flag/pride graphic, 2017.
[Link] [Archive] [Archive 2]
04 - "Transspecies Flag" flag, 2018
[Link] [Archive] [Archive 2]
05 - "Why I call myself Transspecies" personal article, 2018
[Link] [Archive] [Archive 2]
06 - "Gender: Furry II (Now With More Scales)
07 - "Real Dragons: Transspeciesism" article, 2001