I have several cells containing data that have a common denominator that I
want to combine in one single cell with commas to separate the data.

I have tried the following formula (acquired from elsewhere on this blog):

=SUBSTITUTE(IF($A$9="20090501182755",$E$9&",","")& IF($A$10="20090501182755",$E$10&",",""),",","",COU NTIF($A$9:$A$10,"=20090501182755"))

However, instead of returning the data I want, it shows no data at all, not
even an error, just a blank cell.

Any suggestions? Thanks for your help!