Is 70% ethanol hygroscopic?

I'm currently doing some DNA extractions and I realized that in some protocols, they are saying that ethanol is [hygroscopic](https://en.wikipedia.org/wiki/Hygroscopy). 


In [this source](https://www.beckmancoulter.com/wsrportal/bibliography?docname=AAG-666SP.pdf), they are saying: 



> 
> 85% ethanol made with nuclease free water (Note: 85% ethanol is hygroscopic. Fresh 85% ethanol should be prepared for optimal results)
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I know that this is even more pronounced for 100% ethanol. But I'm wondering if 


1. 70% is still "very" hygroscopic so that the concentration might change over time. Say differently, how stable is the ethanol concentration over time?
2. How long would a 70% ethanol solution last? That may depend on the volume made, but I want to know if there could be a "best before" date so that it's no longer considered as a 70% ethanol solution. A year? A decade? 2 minutes?


