Enter formula on last unique value

[CaptainGravyBum]

Once again, I'm stuck on something that's probably simple, but I've been staring at my screen for an hour trying to figure it out.
I need to put a formula in column k on the last unique row (highest count) of the order id - calculated in column I. Column H is already populating only on the bottom row, but that is because it is relying on information from other counts on the sheet (I haven't included all formulas and columns, because it's extensive).

Book1.xlsx
	A	B	C	D	E	F	G	H	I	J	K
1	Article number	Order ID	Delivery date	Carton Qty	Pallet Qty	Weight	Count	Pallets	Unique	Order Count Total	Unique Cons
2	PBB12T	109916	29/05/2024	25	550	385	550		1
3	PBB12T	109916	29/05/2024	25	550	385	550	2	2	1100	1
Sheet1

Cell Formulas
Range	Formula
I2	I2	=IF(B2<>"",IF(COUNTIF($B$2:$B$499,B2)>=2,COUNTIF($B2:$B$2,B2),""),"")
I3	I3	=IF(B3<>"",IF(COUNTIF($B$2:$B$499,B3)>=2,COUNTIF($B$2:$B3,B3),""),"")
K2:K3	K2	=IF(AND(H3="", OR(I3="", I3=1)), 1, "")

Cells with Conditional Formatting
Cell	Condition		Cell Format	Stop If True
I2:I3	Expression	=I2<>""	text	NO
I2:I3	Expression	=#REF!<>""	text	NO
H2:H3	Expression	=H2<>""	text	NO
H2:H3	Expression	=#REF!<>""	text	NO
J2:J3	Expression	=J2<>""	text	NO
K2:K3	Expression	=K2<>""	text	NO
A2:G3,J2:K3	Expression	=#REF!<>""	text	NO

 

[Phuoc]

Try this:

Book1
	A	B	C	D	E	F	G	H	I	J	K
1	Article number	Order ID	Delivery date	Carton Qty	Pallet Qty	Weight	Count	Pallets	Unique	Order Count Total	Unique Cons
2	PBB12T	109916	29/5/2024	25	550	385	550		1
3	PBB12T	109916	29/5/2024	25	550	385	550	2	2	1100	1
Sheet1

Cell Formulas
Range	Formula
H2	H2	=LET(a,COUNTIF($B$2:$B$499,B2),IF(B2<>"",IF(COUNTIF($B2:$B$2,B2)=a,a,""),""))
I2	I2	=IF(B2<>"",COUNTIF($B2:$B$2,B2),"")
H3	H3	=LET(a,COUNTIF($B$2:$B$499,B3),IF(B3<>"",IF(COUNTIF($B$2:$B3,B3)=a,a,""),""))
I3	I3	=IF(B3<>"",COUNTIF($B$2:$B3,B3),"")
K2:K3	K2	=IF(H2="", "", 1)

 

[CaptainGravyBum]

Hi @Phuoc,
Thanks for the reply, however that's very similar to the place I had got to already.
The formula I need is kind of the reverse to your suggestion, I didn't explain it well.

If column H is populated, then the result will be always be "" anyway, but I don't want the other parts of my formula to run unless the unique count in column I is the last/highest number.
So I mean, there are counts running which give the result in the last unique row, so that's the row where my column K formula needs to work.

So, find the last unique row in column I and run some other formula in column K.