Hmm..., grepping with [A-Z]\.\s+\w and a multiline option finds this:

• compatibility.tex:2307:
  A \keyword{struct} is a scope in \Cpp{}, not in C.
  For example,

• support.tex:5906:
  one of these headers in order to be valid ISO C.
  Source files that are not intended to also be valid ISO C

• support.tex:5918:
  The following source file is both valid \Cpp{} and valid ISO C.
  Viewed as \Cpp{}, it declares a function with C language linkage;

• time.tex:2815:
  The UTC time standard began on 1972-01-01 00:00:10 TAI.
  To measure time since this epoch instead, one can add/subtract the constant

These should be "UPPERCASES\@."

We also need to fix cases like

Let \tcode{i} be an object of type \tcode{I}. When ...

I don't know if these are worth fixing or if \frenchspacing can be a realistic option.

Please check first if these actually make a difference to the presentation. I also looked at a couple of such cases where the additional annotations did not affect the visual output.

As far as I can tell, some of these changes make minor differences to the available glue, which may not result in any actual changes.

Sure, I listed only those that changes the appearance. Here is an output of diff-pdf for the first comment. New (old) text is rendered in cyan (red).
spacing.pdf

And here is a diff for the second comment. In that comment, I just picked one example of bad spacing, but actually there are TENS of such spacing (i.e. UPPERCASE}. …).
tcode.pdf

Could you just post a diffpdf screenshot?

Example:

Before:

After:

This looks like an improvement to me.

I have an automated check; 87 occurrences outstanding.