To justify the sub-head oldest I read somewhere that scraps of papyrus, dating back from Egypt 4000 years ago, have been found with central holes in the sheets. Threads of some sort would be used to keep these sheets together ~ and in order. I recall that the sheets were accounts of some sort, which had to be kept together.
The treasury tag is a short length of thread with the two ends sealed in a metal or plastic clasp. I have lived in Cornwall for many years, and the metal ones show signs of rust, which can transfer stains onto the sheets being filed. I now buy only plastic ended tags.
The right-angled ending of the thread means that under normal cicumstances the tag will never pull out of the hole, although the paper can easily tear ~ as it can with any type of punched-hole filing. If papers are to be filed one or two at a time then it is possible to pierce the sheet with the corner of the tag. Small individual sheet paper punches are available at modest cost. I am lucky and have a four-hole punch, which punches such that one of the holes is near the top left corner. It can also punch a dozen sheets at a time.
To protect the filed sheets it is normal to have a thin card cover ~ folded into a folio ~ to wrap around front and back of the pile. To push the tag through both front and back is not efficient. The tag needs to be pushed through one of the covers ~ front ~ or back. If papers are filed sequentially then a choice has to be made about working forwards or backwards. In either case the oldest sheet is adjacent to the cover.
Alternatively separate thicker cards may be used, front and back. If the files are to be stored upright on a shelf then the covers are best cut exactly flush with the filed papers, otherwise the papers will sag and put wear on the corners. In my experience loose covered treasury tagged files are usually stored on the spine or fore-edge ~ upright-sideways ~ inside hangars in a filing cabinet.
For many years I have worked in companies who store their every day files in treasury-tagged folders. Their lack of bulk was a huge advantage for the messengers, whose daily rounds were delivering piles of papers. I have noticed, in hospitals I have visited, crates os such files being pushed around in trolleys by such messangers. The ease and ecomony of filing in this way can lead to lots of paperwork being shunted around. A tricky trade-off between excellent communications and overdone paperwork.