cannot convert text to number?

I have a spreadsheet of data exported from and ACT database - and it has several issues that make it hard/messy.
One is that it adds an extraneous NL to each field, and another is that it prepends an invalid character (code=63) to numeric's.

Each of these are fairly easy to correct, bu I end up with some cells that all look empty, but are not formatted as numbers, and I cannot seem to easily convert them.

I attach an example. The issue is that actual number cells convert fine, and I can then do arithmetic on them.
But blank cells, do not work well. The result of the cleanup (=mid(clean(A1),2,99) for blanks looks empty, and tests as isText(), but gives a #Value error on trying to convert it .

So I tried a formula where I would leave blank cells alone, and just try to convert number cells:
=IF(ISBLANK(C2),,VALUE(MID(C2,2,99)))
Which converts empty cells (really empty, I manually clear them) to 0 values, and cells that have resulted from a clean+mid but look empty give an error.

So the basic question is:
* What is in the apparently empty but not convertable (value) cells like C4 (=C22) (the user named cell "G11" )?
Note that manually clearing them, then it works to be convertable to a numeric, but gives a zero (instead of blank).
* How should I be converting these to numerics? (I want to do sums on them).