I have one column with both text and numeric entries. What formula can I use
to count the # of uniques, disregarding any cell that contains the word
"Unknown" or is blank? For example, in the following, I should get an answer
of 2 (which would be AB123 and GF999). The answer is probably something I
will be embarrassed that I couldn't figure out.....

Cell A1 Unknown
Cell A2 AB123
Cell A3
Cell A4 GF999
Cell A5 AB123
Cell A6 Unknown
Cell A7 AB123