In December, 2019, a report was being made in my school district; the Oregon Department of Education allegedly wanted to know: "What language was my primary language?"
I wrote the following answer:
"I was born in Mexico, and learned Spanish as my primary language in my earliest years. I entered first grade, in the U.S., without knowing much English; elementary grade instruction in English was way over my head and unintelligible to my Spanish-trained brain."
"I had dual (U.S.A. / Mexican) citizenship because my dad was a U.S. citizen, (he was born in Los Angeles, California).
I was also simultaneously exposed to English in my later years as a child, as I learned to speak to my dad & my brother in English. With my mom, I spoke in Spanish."
"ODE language experts should know, & be familiar with, the term called "simultaneous bilingual", which best describes my upbringing, in terms of my linguistic development as a child."
After reading your entries in the discussion above, I conclude that I was both a simultaneous & a sequential bilingual. Simultaneous, because my dad spoke English to me as a child, and vice-versa, but also sequential because by 6 or 7 years of age, I was not conversant in English, and the public schools compelled me to learn English. Yet in those formative early years, 7 - 10, I had only learned conversational Spanish, while at school I was learning grammar, writing, reading, etc.
Which goes to show that definitional terminology, even in linguistics, is sometimes like throwing labels at people, which only give a partial understanding of the complex realities in which people develop and grow.