MATCH or VLOOKUP multiple columns with text

Thanks for any help in advance.

My issue is this:

I have multiple columns with names. I want to cross reference each of these cells (names) with all other cells to see if they occur more than once.
For instance, I want a formula that will look in the range specified and return to me the cell address or addresses of all occurrences. The below example would return "A2, C3" for occurences of "Bob, A" not counting the first occurence.

A B C
1 Bob, A Fred, D Alex, T

2 Bob, A Stacy, J Alicia, S

3 Man, B Ted, B Bob, A

I have tried using =ADDRESS(MATCH("ABC",A:A,0),2) for example to no avail. I am running into the problem that the match function only works on one column at a time. I have 20 columns of names. If you are wondering why, they are authors of scientific papers and are listed in order of 1st author to last.

Thanks again!

Bump bump bump

Do you mean a concatenation of all names in one column? I can do that. Attached is a sample of my data. The countif() might come in handy later so thanks for that!