Security :: Strategy For Multiple People To Edit Different Records On One Page?

I've been developing a database system that stores test results from two different machines. (It's a foundry, each machine tests for the amounts of a collection of elements in a piece of metal. One machine does the tests on iron, the second on aluminium. Both produce the same list, but each machine will have much more of some elements than others.)

I used folder security to limit who has access to what folders, so there is a general page for anyone to view results from any machine in the root, one folder has a page to allow people in a particular group to edit/correct the iron results, and a second folder has a page to allow another group of people to edit/correct the aluminium results. Now, we've picked up a third machine which tests aluminium samples too, and it belongs to a third group of people. What is the best or recommended method to allow this third group to edit samples from the third machine only?

1) Should I have a third folder, and copy in the page from the other aluminium folder, and tweak it so it only shows and allows edits to results from this new machine? This seems like the quickest, easiest method, but a waste of effort as it's mostly duplication of existing work.

2) The other option I see is to keep one aluminium editing page, but to limit the results that are shown to the ones that the current user should be allowed to see. (One page which shows one group of people one half of the results, and shows a second group of people the other half of the results). Is there a way to achieve this that is almost as easy as using folder-based permissions?

3) Is there another way that I'm missing?