It's not some thing I read in an article or any thing like that. It's all just stuff I have learned from being really involved with the 7th gen Celica, I bought my 2000 GTS some time in late 1999 and I immediately started modifying it. Primarily because I was modifying the car, I wanted to learn every thing there was to know about it, so have been reading up about the car on forums/articles for the past 3 years and almost every available modification has been personally done to my car, so I just know a lot about this stuff in general. Most of the information that I have learned about the Celica was from NC.org.
In the specific case of the ECU over riding the SAFC, I remember first becoming aware of the problem when NC.org member cool2mike was trying to use SAFC to tune a custom fabricated turbo system on his GT. He did 30 dyno runs trying to tune his car which proved to be an impossible task because the ECU kept compensating for the adjustments. Because this compensation was visibly proven on all the dyno run print out's, people could no longer ingnore the possibility that the SAFC was, in fact, worthless on a 7th gen Celica. Through other multiple posts that were made over time, people figured out what was actually going on in regards to false MAF votages and OBD11.
I'm sorry that I don't have a specific article to refer your to, or a specific source of information to support what I am saying. I will say this - I would never submit any information unless I felt that it was all 100% accurate because I know how false information can effect the end user, especially in regards to making important and some times expensive decisions when modifying your car. I am honestly just trying to help people out here.
I'll bet that cool2mike, for example, would have appreciated knowing about this before he spent all the money on 30+ dyno runs.