The sense of Small Caps could be to have the lower case in the form of upper case and the sense of Petite Capitals to have the upper case in the size of the lower case (more or less).
As long as it is |A| and |a|, the situation is clear.
But when am I dealing with glyphs that seem to have no such alternative? I refer for example to U+01BB, U+01BE, U+01C0-3: how are these glyphs to be understood? Does it make sense to produce a .sc or .pc version?
I see that in Brill font there are many glyphs rendered as SmallCaps, but they don't run out of all lowercase letters. On the basis of which criterion was the choice made?