Fill Empty table cells with previous values

Dear community, have the following tables.

• Table 1 - Calendar Table (Jan 2020 --> Aug 2023)

• Table 2 - Sales Data (Sales Date contains multiple items). for the screenshot below, i have filted one particulare #item 1.. 

when i combine my calendar table and sales table including sales price it will look like: 

for all months with sales of #item 1 i see an empty cell.  if i would like to compare Aug 22 with Aug 21 i doesnt work because Aug 21 doesnt have a data point / no values. in reality the price of #Item 1 was 11,00 $ i just didnt see it. 

Goal: would like to calculate the difference between Sales Price today vs. Sales Price Previous Year.  Like Screenshot below

would like to fill empty cells with Sales Price out of previous months when sales were made (yellow marked cells).

thanks for your help in advance

Mike