Qs on free variable occurrences

["Drew Adams" <drew.adams@oracle.com>]

Consider variable `minibuffer-history-position', in library simple.el.

1. It is bound (`let') in function `repeat-complex-command'.

2. It is assigned a value at the top level of the file.

3. It is both used (evaluated) and assigned a value in functions
`previous-matching-history-element' and `next-history-element'.

4. Byte-compiling the file gives no warning of the variable being used as a
free variable (in #3 and #4).

This is not a criticism, but a couple of questions.

a. Why #4? Is it because the byte-compiler cannot detect these as free
occurrences of the variable or is it intentional (TRT)? If the latter,
what's the rationale?

b. Is this coding style considered good or bad? In particular, should
`minibuffer-history-position' be declared a global variable by giving it a
defvar?

Just trying to learn. Supporting reasons would help me understand. Thx.