To avoid the need to get the date format correct, I like using... I think I first saw it in a post by troyansky? Apologies if I'm improperly attributing it, and apologies if I get this syntax a little wrong. I'm eternally slightly messing up my set analysis and needing to fix it.
I don't know if a variable defined as you have it will keep that format. Probably, but I'm not certain. But with the above, you don't have to worry about format, so it should work regardless. And you could also define it something like this, with no formatting at all:
LET vCalcDate = makedate(2016,8,31);
Nothing wrong with what you have now, though, at least that I can see.
John nailed it right - using the Advanced Search is preferable compared to Simple Search because you don't have to worry about formatting your dates in a particular way.
The only addition I could offer is this - another advantage of the Advanced Search is that you can use your Variables without the $-sign expansion, and that is another possible problem that can be avoided. So, the best syntax in this case is this: