Store my data and compare it automatically with old data before refreshing

I've linked my dashboard with excel sources and i designed the whole dashboard, but i'm just missing the main request that i received from my managament. 

We need this dashboard to compare or old data (before clicking refresh button) with or new data ( after clicking refresh button) to tells which area has new changes and what's the difference exactly? 

for example : i have a bar chart with 20 patents for march and when i refresh on april i had 18 patents only, i want to know exactly what happend in the last month's patents'. which department withdrew thier patent? 

i hope it's clear enough 😣😣😣😣.