Which is correct or better?
- The graph shows the shipment volume since Sep 2003
- The graph shows the shipment volume from Sep 2003
"since" sounds better. If you use "from," you risk confusion from someone thinking that you only have the volume from September 2003, not from all months prior to then. However, the word "from" is often used colloquially, at least in the US, to mean "since."
I would use "from" because a period is from... to...
I don't recall ever seeing "since" used that way, particularly for financial reports, but it is possible.
"at 30 September 2003" would mean at that point in time.
"for September 2003" would be for that month.
"From" is definitely used the most according to what I can see from looking through official documents relating to business statistics.
If you refer to say things like weather statistics, it would be more usual to say: "Weather records show that world temperatures have slowly risen since the 1970's."
"The graph shows the shipment volume since Sep 2003"
I think it is more natural to remove the second "the":
"The graph shows shipment volume since Sep 2003"
I believe that gives the intended meaning. Now, using "from":
"The graph shows shipment volume from Sep 2003"
To me, it is ambiguous whether that means Sep. 2003 only or from Sep. 2003 until now. For the latter, I would say:
"The graph shows shipment volume from Sep 2003 onwards"
I beleive "from" is more appropriate and sounds better.
I think "from" is better because it shows a period of time.
Using "since" can be confusing because somebody reading it might think that the graph only shows the shipment volume since september and that's it ,unless that is what you mesn.