There is no right or wrong answer when it comes to submitting an individual set of supporting documentation (fingerprint cards, trust copies, responsible party form, etc.) with each individual NFA application.
There are plenty of folks who historically have sent in multiple applications with one set of supporting docs and gotten all of the applications approved. So in this regard, yes... there is no shortage of historical precedent of applicants who have only sent in one set of supporting docs and gotten multiple applications approved.
However there are also a subset of those applicants who only send one set of supporting docs with multiple applications where it doesn't all go to plan. They end up having applications split up, examiner woke on up on the wrong side of the bed, etc. and they end up getting 1 out of 4 applications approved or 3 out of 4 approved, etc.
Sometimes these applicants are contacted by the NFA branch to let them know of the issue and/or the applicant finds out because they called the NFA branch to check on status. If the issue is caught in time the NFA examiner is sometimes able to use the recently approved applications prints/docs to clear up the remainder of the stuck applications, sometimes applicants have to send another set of supporting docs to the NFA branch, and other times applicants find out when applications come back disapproved with little to no recourse but to start the process over.
So the question really comes down to, what level of risk do you want to take to save money by not sending a complete set of supporting docs with each application? I do believe the odds are in your favor given the number of success stories out there but I also know its not a 100% risk free option either based off a minority of problems reported as well.
For me personally fingerprint cards are essentially free (the ATF mails as many to me as I want and I roll them myself) and paper/ink from my printer also cost almost nothing.
So given there is almost no meaningful cost implication for me personally to send a complete set of supporting docs with each application, that is what I have always done. I prefer to maximize my odds of success on each application when the approval process timeline is measured in months (or more) and I am dealing with a government agency that can be challenging, unpredictable, and with few options in the way of recourse if I don't like the outcome. Again for me, why take the risk of problem and potentially have to start all back over, even if its a small risk over a couple extra fingerprint cards, etc.
The one thing I have never heard of is somebody having problems or getting denied because they sent in a full set of supporting docs with each application.
Now if you are somebody who pays their local PD $20 per print card, purchases passport photos at $5 per picture at wal-greens, you don't own a printer and pay 5 cents a page at Kinkos to print, etc. than maybe the cost savings vs. risk is totally worth it to bundle up multiple apps with one set of supporting docs.
Each applicant will have to weigh the pros/cons for themselves.