Two honest lists can differ

The instinct, and why it misfires

The instinct is that one of them must be lying. It is a reasonable instinct in most contexts, where two accounts of a fact should match if both are honest.

It misfires here because the underlying object changes without notice and both copies were made at unknown moments from unknown sources. Difference is the expected outcome, not the surprising one.

The four ordinary reasons

1. They were copied at different times, and the set changed in between.
2. They came from different sources, each of which was itself a copy of a different moment.
3. One has been pruned of quiet routes and the other has not, which is an editorial choice rather than an error.
4. One has been added to from somewhere less careful, which is the case worth noticing.

Why the fourth is the one to watch

The first three produce lists that are subsets or supersets of each other in a boring way. The fourth introduces a string that was never in the set at all, and it is exactly what a list longer than the set describes.

So the useful question is not which list is right, but whether either contains something the other has never heard of.

What agreement is worth

Two independent sources agreeing on the same small set is mildly reassuring. It suggests both copied from something similar, which is weak but not nothing.

It is not proof, and it can be produced by both copying from the same upstream source without either knowing. Independence is hard to establish and easy to assume.

What disagreement is worth

Almost nothing on its own. It tells you the copies were made under different conditions, which you already knew.

It becomes informative only when you look at the shape of the disagreement: missing entries are unremarkable, extra entries are the thing to examine.

The comparison that is actually cheap

With a small set, comparing two sources takes seconds. Read across the strings, not just the first characters, and note whether either has an entry the other lacks.

This is one of the very few checks a reader can perform that requires nothing but attention, and it is available only because the set is small. See why the set is three and not fifty.

What to do with the result

• Both agree: keep what you have, mild reassurance, nothing more.
• One is missing an entry the other has: unremarkable, keep the fuller set, nothing follows.
• One has an entry nobody else has: that entry is the interesting object, and the burden of explanation is on it rather than on you.
• They share nothing at all: something is badly wrong with one of them, and the answer is not to average them.

The tone to keep

Not suspicion of every source, which is exhausting and produces no decisions. Just an accurate sense of what a list is: a copy of a moment, made by somebody downstream, which is what makes disagreement ordinary rather than sinister.

The comparison in practice, in about twenty seconds

Open the source beside your own copy. Read each string from its tail rather than its head, since the tails are where they differ. Note whether either side has an entry the other lacks.

Missing entries are unremarkable and need no explanation. An extra entry is the whole result of the exercise, and it is worth more attention than everything else on either page combined.

This is one of the very few things in this subject that a reader can genuinely check, it requires no tools, and it is available only because the published set is short enough to hold.

What this study is not. It is not an accusation against anybody, and this site does not compare itself with other pages or assess them.