Problem with getting CONCATENATE text combined with an IF/THEN and nested VLOOKUP to display...

So as I mentioned above the line:
IF(AND(U12>0,T12>0),CONCATENATE(VLOOKUP($U$12,W290:X299,2)," ",VLOOKUP($T$12,W304:X313,2)),""))&CHAR(10)&CHAR(10),
is also TRUE because text values are > numbers so AND(U12>0,T12>0) resolves to be TRUE (again highlight that part and you will see TRUE in the 'bubble') and that line does NOT concatenate the "P.S., " before the VLOOKUP result and is why you weren't getting that P.S. part before. Now you are getting the correct line T12=" " AND the incorrect line T12>0.
You can fix it by adding the check or if you never have 0 just replacing it with ISNUMBER(T12).
As for the difference between "" and " " let's think about a balloon that you take out of the bag that isn't inflated and the balloon after you inflate it. I would call both a balloon but they certainly aren't the same.

Another way to look at it is that don't you think

"     " is different than " "

because the former has a lot of spaces while the latter is only 1 space so why wouldn't you think "" is different than " "?