Parsing Data and Comparing two string in arduino
I think that the biggest problem that you are encountering is that reading a line from serial is not as straightforward as you would like. I don't have a quick and easy solution for you, but there is much on this issue that you can look at. 

You have two serial read while loops. The first exits as soon as there are no characters to read (even though some may be on the way). When "\n" is read, you set parsing but it does not mean that \n is removed from dataIn.

The second serial read while loop is using a delay(3) after detecting that a character is available, but that character could have arrived after the first read and be the only character in the buffer, for example.

I suspect that the reason that your String comparison does not work is simply because the Strings are not equal.

Your String looks like something read from an HM-10/11 or something similar. I have had some success reading those transmissions by doing the following:

Make sure the serial buffer is empty. When a character is available, read it into your building String, but continue looking for characters that are available for a set amount of time (maybe a couple of seconds). Continue looking for characters until the time has elapsed and not as soon as there are no characters available (because more may be coming). Alternatively, keep building the string until you recognize the "DISCE" marking the end of that transmission.

A problem, however, is that, in my experience, if it is a very long line (that can occur when there are many devices out there), you will never get that "DISCE". I assumed that this was a firmware issue.

Hope it helps.