INDEX formula error - using SMALL, ROW, MIN

I have a formula that is meant to go through a column of data and pull every match to the searched number. I then have an array where it pulls the corresponding data (Looks in column A and returns column C, etc.). So it needs to find the first match and all it's data, the second match and it's data, etc. However right now it is not pulling ALL matches. It is pulling a random (?) number of them. The complex formula is:

=IFERROR(IF(INDEX(Data!J$2:J$20000,SMALL(IF($A$2=Data!$A20:$A$20000,ROW(Data!$A20:$A$20000)-MIN(ROW(Data!$A$2:$A$20000))+1,"")ROW(Data!$A20)))=0,"Not available",INDEX(Data!J$2:J$20000,SMALL(IF($A$2=Data!$A20:$A$20000,ROW(Data!$A20:$A$20000)-MIN(ROW(Data!$A$2:$A$20000))+1,""),ROW(Data!$A20)))),"")

The heart of the formula is :
INDEX(Data!J$2:J$20000,SMALL(IF($A$2=Data!$A20:$A$20000,ROW(Data!$A20:$A$20000)-MIN(ROW(Data!$A$2:$A$20000))+1,"")

Any ideas?