Capital gains.  For any of those 20 years were property taxes previously deducted?

The question isn't whether the taxes were deducted, but whether an election to capitalize them was filed for any of those years.  

I know that this is not even remotely related to this question, but I thought it was remotely related to this question and I am weird, so here goes.

Can we then deduct unrealized losses?

Highly doubt taxes were capitalized. However, the couple are very detailed and likely could go back through twenty years of taxes to determine if property taxes had been itemized and/or claimed on their State taxes. Is there a way for the software to document that? 

Happy Friday. 

p.s. Definitely sharing the comic relief with a certain someone. 😉 

"..... whether an election to capitalize them was filed for any of those years. "

Don't overlook @BobKamman  's comment, even if your clients can determine whether deducted or not in the prior years.