Dates from an IF statement

Hello,

I ve selected some dates via a simple if statement and can see the dates in the cell where I want them. But when I try to use them in another formula it doesn't recognise them as dates regardless of how I try to format them. Can anyone help?

I get the date from one of two columns of dates with:
=IF(H623="",R623,"")
then try to use them with:
=SUMIFS(Spend_Tracker!N141:N10138,Q141:Q10138,Q261,S141:S10138,"=Sep-15")

thanks