Firstly, as a reminder, the [!] flag is initially used for CD dumping and not for floppy disks. It is found in very few datfile on the whole of the main TOSEC branch (Amiga and C64 first).
There is no precise protocol for determining whether a dump is perfect and unmodified, but the multiplication of converging sources helps in the decision.
I also developed ADF-Workshop for this reason. It allows you to see clearly if one disk stands out from the others among all the disks in a given production.
I currently have more than a million ADFs in my database for only 340k unique disks.
To tell the truth, a single raw dump could be enough if we had the right tools to analyse it (those of SPS), but we don't...
The other parameter to take into account is the level of confidence you can place in the sources.
It's easy to make a copy of a source available on the Internet and incorporate it into your collection, while taking ownership of the extraction. The same is true of archive.org, where contributors remain vague about the origin of the digital copy of a medium (it's easier to take a photo of a disk than to extract its contents).
I'm bound to have more confidence with a regular contributor, where the "dump of an original" indication will have more value and where the number of identical copies will be less restrictive.
The media also plays a role, NoDOS disks are less prone to system alterations (which is normal), but when they do occur, it's easier to get identical altered disks.
In short, it's a case-by-case decision, based on the existing data, the disk (true original? Purchased on ebay? ...), the dumper, the archivist's experience and ... feeling.
For the moment, we can say that 3 identical copies outside TOSEC is a good level of confidence.
If there are fewer, we'll have to take a closer look at each candidate.
