Filter on Self Join

Please I have a scenario, where I get snapshot of a db every day (merge the files into one table).There are different questions that could be asked on different files, although we are particular about 4 specific timelines, for example second week of every month(that means we will have 12 of that scenarios in a year). I am trying to check for changes of date on records for different snapshot date. 

I have seen different examples where the table is duplicated in the model then joined back on itself , but this does not work for me.

The approach I took was to pass the records of the time line into a variable then inner join on them, but the chalLenge I had was to filter on the variable tables to check where the dates in the opportunities are different

ideally in SQL where current date <> previous date

ChangedDate =
VAR
Latestopp =
CALCULATETABLE(
SELECTCOLUMNS('Income',
"Company",'Income'[Company],
"TC",'Income'[TC],
"Product",'Income'[Product],
"Name",'Income'[Sales Name],
"Oppid",'Income'[Opportunity],
"Current Date",'Income'[Date],
"Current Sales",'Income'[Sale]
),
'Income Status'[Load Status] = "Latest"
)
VAR
prevopp =

CALCULATETABLE(
SELECTCOLUMNS('Income',
"Company",'Income'[Company],
"TC",'Income'[TC],
"Product",'Income'[Product],
"Name",'Income'[Sales Name],
"Oppid",'Income'[Opportunity],
"Previous Date",'Income'[Date],
"Previous Sales",'Income'[Sale]
),
'Income Status'[IsYear] = "yes",
'Income Status'[P_Week Indicator] = "1"
)
VAR
IJOIN =
NATURALINNERJOIN (Latestopp,prevopp)
var
datechange =
CALCULATETABLE(LJOIN,
)

)

Please any advice on the dax above. Thank you