Calculating measure for non-existent data

Hi all, 

I'm working with Power Pivot but since it's DAX, it should be the same as working with Power BI I hope. 

My problem deals with missing data in my dataset. 

Let's say I have 2 month's worth of data, Dec'23 and Jan'24 and the dataset contains a list of accounts with month end balances. 

My goals are to calculate the total net change in balances, the total change in balance for accounts that increased month over month, and the total change in balance for accounts that decreased month over month. 

For example, let's say there are 3 accounts: A, B & C.

The total net change is -5, positive change is 3, and negative change is -8.

My previous month balance measure =CALCULATE(SUM(RepricingData[NetBalance]),PARALLELPERIOD(RepricingData[ActualDate],-1,MONTH))

My net change in balance measure =

VAR CurrentBalance = SUMX(RepricingData,RepricingData[NetBalance]) + 0

RETURN CurrentBalance - [Previous Month Balance]

The measure in the total row is correct, but when I try to calculate the measures for positive and negative changes, it doesn't work. 

I think the issue is with accounts that had a balance in Dec, but doesn't exist in Jan as per below:

The change from previous month measure should be -736.38 but since there isn't a Jan data point for this account, it's returning a blank. 

What would be the best way to correct this? I've tried the following examples and it does not work:

https://community.powerbi.com/t5/DAX-Commands-and-Tips/Dealing-with-Measure-Totals/td-p/63376

https://community.powerbi.com/t5/Quick-Measures-Gallery/Measure-Totals-The-Final-Word/m-p/547907

Thank you.