insert new column for each sheet & create report

[Alaa mg]

hello
I have two sheets present data for each month and every month will add new sheet contains data for each month . so what I want create the whole report in sheet merging based on the others sheets. so I put the result in sheet merging how should be , with considering should update data in sheet merging based on others sheets .
if the item is repeated for next month then should add value to the next cell in the next month and if there is not item existed in month but is existed next month then should add - for the month doesn't contain item .
note: I add new sheets with the same structure every time with about 1000 rows across sheets
sorry if the detials are poor but the result hope to be clear

1 (2).xlsm
	A	B	C
1	ITEM	ID	QTY
2	1	MT ASGL-VEN SD-1	12.00
3	2	C-ZER	130.00
4	3	BB 2000MN TT GH	90.00
5	4	BD 234 NH GG	78.00
6	5	DEWR 1222** SS TF HJK	34.00
7	6	BR 111/33M ER HJ	66.00
8	7	VB 1222** SS TF HJK	45.00
SH1

1 (2).xlsm
	A	B	C
1	ITEM	ID	QTY
2	1	MT ASGL-VEN SD-1	10.00
3	2	C-ZER	15.00
4	3	BR 111/33M ER HJ	80.00
5	4	VB 145** SS TF HJK	45.00
6	5	DEWR 1222** SS TF HJK	34.00
7	6	DAS 1222** SS TF HJK	35.00
8	7	TRM 2000MN TT GH	16.00
9	8	BD 234 NH GG	70.00
RP1

result

1 (2).xlsm
	A	B	C	D
1	ITEM	ID	MONTH1	MONTH2
2	1	MT ASGL-VEN SD-1	12.00	10.00
3	2	C-ZER	130.00	-
4	3	BB 2000MN TT GH	90.00	-
5	4	TRM 2000MN TT GH	-	16.00
6	5	BD 234 NH GG	78.00	70.00
7	6	BR 111/33M ER HJ	66.00	80.00
8	7	VB 1222** SS TF HJK	45.00	-
9	8	VB 145** SS TF HJK	-	45.00
10	9	DEWR 1222** SS TF HJK	34.00	34.00
11	10	DAS 1222** SS TF HJK	-	35.00
merging