It can prove a lot if you take other things into account.
We have accounts that belonged to different people in the past and were sold in the same year.
They applied into signature campaigns, started posting in a very similar manner, making the same spammy 1-2 sentence posts with the same mistakes.
Next, they took exactly the same break in posting, followed by waking up on the same day and applying to the same signature campaign. They even made the same mistake in personal text when they applied. Now, you've found proof of them sending coins to the same address.
On top of it all, the accounts that we called out did not even try to explain the coincidences. GreatOrchid, hahahafr and uszaty43 are not posting anymore.