You're welcome! I also made an edit to this post since you commented, because I dug into the alt.sexual.abuse.recovery archives, which go back farther, to see if I could find an earlier use of "system," and I did! By a multiple who rejects the MPD label no less! (Which is nice, I am really uncomfortable relying on those old BBS records.) On March 7, 1992 (so the second-earliest date I've got), Hineni said:
"I adhere to the 'Internal Family Systems Model' (which title is quite misleading) that asserts instead of a monolithic personality (ie one 'I' as our 'ego'), we all have a multiplicity of parts inside (and one unique part called a 'Self'). [...] We all have a number of different parts (or subpersonalities) which coexist in an ecological system. [...] in my view we all have multiple personalities; only extremely polarized systems qualify for the term MPD (which term I dislike anyway)."
So it looks like non-MPD/DID plurals have been using the term "system" for over thirty years.
Re: Thank you!
"I adhere to the 'Internal Family Systems Model' (which title is quite misleading) that asserts instead of a monolithic personality (ie one 'I' as our 'ego'), we all have a multiplicity of parts inside (and one unique part called a 'Self'). [...] We all have a number of different parts (or subpersonalities) which coexist in an ecological system. [...] in my view we all have multiple personalities; only extremely polarized systems qualify for the term MPD (which term I dislike anyway)."
So it looks like non-MPD/DID plurals have been using the term "system" for over thirty years.
--Sneak