Why are you persisting with the LEFT function? Surely you could use:
IF(B16=42185,1,0)
You'd only need to use:
IF(INT(B16)=42185,1,0)
if the value in B16 might include a time component.
In either case, the fact the date in B16 might be calculated makes no difference.

As for
I did say 42185 was the value for 30/6/2015. If you want to disregard the year component, you could use a formula like:
=IF(AND(Month(B16)=6,DAY(B16)=30),1,0)
Again, the fact the date in B16 might be calculated makes no difference. In this case, neither does the possibility that the date might include a time component.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]