The website gives 一 and 不 as two of the three ‘essential’ tone changes everyone should know: meaning there are lots more out there.
I am aware that these are special cases. But, why are they not written in their original forms? Even the website states this:
Why Tone Changes Are Not Written
Normally the tone changes above are not written in the pinyin; you are supposed to just know the rule and apply it if you say the word(s) aloud. The reason for this is that in many cases if the tone change is written, you will be confused as to what the “normal” tone of a character is actually supposed to be.
For example, you might wonder, “is this a third tone written as a second tone because it’s followed by a third tone, or is this character always a second tone?” Always writing the original tones solves this problem. But it also means that you really need to know your tone change rules. Learn them well!
This is exactly what I meant in my first question.
Maybe if I phrased it differently: there are four instances I found where words which have tone changes are not written (which is the standard way), but I found an outlier (不是) in which the tone change is written. Why is that?