Why would you expect this? First you are using inspection points with an 01 inspection type I think since the lot number starts with a 1 and that is standard SAP numbering. Unless you have changed it. Inspection points were originally designed to only be used with 03 lots for inprocess testing. It was only later that you can use it for other inspection types. Physical samples is similar to inspection points and you can use those with other inspection types.
But in your case, you must of received in 315, so that is always going to be the number to inspect. Jut because you choose to use inspection points, doesn't mean SAP is designed to track the remaining amounts across your sampling points. It was never designed for that.
I can see how you would want to use this as it appears your inspection spans multiuple shifts and you want to track the inspection by number of units inspected each shift and have the number of units still to be inspected to decrement after completion of each point.
I'm not sure there is a good way to do that.
There are ways to create your own sampling procedure calulations. in config, you set up a new determination rule using a samplin scheme. Then create a new sampling scheme for it. Instead of using FM QDRS_SAMPLING_PLAN_SAMPLE you would copy that FM to a new FM. Then insert your own logic into that custom FM. You would need a sharp progammer I believe but I think you should be able change the total sample qty by subtracting the qty already tested in previous inspection points from the quantity of the inspection lot passed in. I don't think doing this hurt the final UD process.
If you use 100% inspection, copy and modify the FM used for that instead, QDRS_100_PER_CENT_SAMPLE.
Craig