Count unique instances in one column meeting multiple criteria (with OR condition)

I've read most posts on this forum for this topic, but still can't seem to get my formulas to work. The answer may be a pivot table, but I'd like to at least know I've tried all my options.

OK - the spreadsheet actually has 17 columns, but I can't do any of the other calculations without being able to get this one right, so I'm only including these two for now.

Column A - Position
Column B - Grade

- Count unique instances in Column A that are either "O*" or "W*" in Column B

- Count unique instances in Column A that are "E*" in Column B

I don't think wildcards can be used though. I can get it count unique instances (=SUM(IF(FREQUENCY(A2:A48,A2:A48)>0,1)) - but it doesn't seem to work when I try to add multiple criteria.

I've attached the most basic example of what I'm looking for. Any help will be greatly appreciated!