Running Costs of Inventory depending on two dates

Hello,

We buy and sell vehicles and need to show what the value of inventory will be in each month. In my work book for each vehicle i have a cost and a Into inventory date and an out of inventory date. across the top i have the first day of moths for the next 14 months. currently my formula is (this is from O2 but is the same thru to AC2) =SUMIFS($K:$K,$L:$L,"<="&O1,$N:$N,"<="&O1)

It makes sense why it isn't working because the OFF FP (out of inventory) is before the date in O1, but i need to be be counted in O1 as it will be in inventory then. Any ideas? Thanks


Screenshot 2021-08-04 143622.png

Please see attached workbook. Thank you.