The company was founded in November 1990 as Advanced RISC Machines Ltd
and structured as a joint venture between Acorn Computers, Apple,
and VLSI Technology.
The comment implies, though, that they get a special deal because they are a founder. Neither Wikipedia nor the linked articles say that.
There won't be a source because the details of the current commercial contract between Apple and Arm will be highly confidential.
In any event, it's vanishingly unlikely that Apple gets some special unique rights to IP created in the 2000s as a result of having a big shareholding in Arm in 1991 which they sold completely in the 1990s.
Yes, Apple probably gets a great deal but because they are a huge, enormously high-profile customer who has worked closely with Arm on the development of their latest IP.
Also this deal until 2040 (signed nine months ago) is crazy. I can't imagine why Apple would sign such a thing unless they got really phenomenal terms.
And why would Arm give such amazing terms?
Not because Apple was an Arm founder 35 years ago.
It's probably because Apple showed Arm a prototype of a Mac or iPhone running on "Apple Silicon gen 2" aka RISC-V.
I think your analysis sounds good: Apple certainly gets special deals, but those deals don't have anything to do with having been a major share-holder of ARM some 30 years ago.
Thanks for your comment on the analysis. I see this all the time, often in even more extreme form, such as Apple gets it all for free! You can look at Arm's accounts in the 1990s and prove that Apple never got it for free.
> ... we have entered into a new long-term agreement with Apple that extends beyond 2040, continuing our longstanding relationship of collaboration with Apple and Apple’s access to the Arm architecture.