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If you look at 2016, they never staked in Nov/Dec (and July IIRC), which would carry over into 2017.
I'm not near a PC right now, but if you have the chance I would suggest averaging the daily earned over a 36 month period. I would expect it to average out to (I think?) ~1k a day.

I've made the relevant excel sheet for 2016 as well so we have:

So when I combine them I get

That is very close to the Gridcoin stats estimate for the wallet's GRC daily interest owed.
Thank you all things cleared! :)

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