SUMIFs to return a 0 or N/A if values not found

=IFERROR(SUMIFS('Period 2 AUM Data'!$AH:$AH,'Period 2 AUM Data'!$A:$A,B30),0)-IFERROR(SUMIFS('Period 1 AUM Data'!$AH:$AH,'Period 1 AUM Data'!$A:$A,B30),0)

Unless you prefer:

=IFERROR(SUMIFS('Period 2 AUM Data'!$AH:$AH,'Period 2 AUM Data'!$A:$A,B30)-SUMIFS('Period 1 AUM Data'!$AH:$AH,'Period 1 AUM Data'!$A:$A,B30)),0)


Iferror is a VERY simple formula:
http://chandoo.org/wp/2011/03/11/iferror-formula/

SUMIFS won't return an error if the criteria isn't found.......it'll just return zero so I'm not sure that IFERROR will help....

Try using COUNTIF to check if the criteria is present, i.e.

=IF(COUNTIF('Period 2 AUM Data'!$A:$A,B30)*COUNTIF('Period 1 AUM Data'!$A:$A,B30),SUMIFS('Period 2 AUM Data'!$AH:$AH,'Period 2 AUM Data'!$A:$A,B30)-SUMIFS('Period 1 AUM Data'!$AH:$AH,'Period 1 AUM Data'!$A:$A,B30),"N/A")

try and see if this works:

=IFERROR((1/(1/SUMIFS('Period 2 AUM Data'!$AH:$AH,'Period 2 AUM Data'!$A:$A,B30)))-(1/(1/SUMIFS('Period 1 AUM Data'!$AH:$AH,'Period 1 AUM Data'!$A:$A,B30))),NA())