Another answer states that:
The common law position is that the finder of a chattel acquires a title that is good against the entire world except for the true owner.
Is there a term for this doctrine of the common law?
This common law property concept is sometimes called the "finders principle" or even sometimes simply "finders keepers." See e.g. Skrypnyk (Liddiard) c. R., 2014 QCCQ 21445, at para 43.
But courts are critical of that shorthand because it misses some of the details that would be in a full presentation. See e.g. Hanna v. Gulf Log Salvage Co-operative Association, 1978 CanLII 326 (BC SC), at para 14. Even the more detailed statement you have quoted from a previous answer of mine, much like the statement by the judge in Hanna at para. 14, is still not the full story (although adequate for their purposes in those contexts).
A full description would be something like this:
Orthodoxy has it that the finder of a chattel acquires title that is good against the entire world except for the true owner. That oft-cited proposition is a little misleading. Not all found property is necessarily presently owned. A recovered item may have been abandoned by its previous owner. An abandonment involves the converse of possession-taking: there must be an intention to relinquish title; that is, an indifference as to the fate of a chattel, coupled with sufficient acts of divestment. It is self-evident that a finder of ownerless property can face no superior claim. In addition, it is not only the true owner who may assert a prior right, but anyone with a valid a subsisting entitlement, including, theoretically, some previous finder. Therefore, a more accurate general proposition is that a finder acquires title good against the world, except for those with a continuing antecedent claim. That is a general statement about the relative rights of owners.
(Thomas v. Canada (Attorney General), 2006 ABQB 730 at para 36, quoting Bruce Ziff, Principles of Property Law, 4th ed. (Toronto: Thomson Carswell, 2006))
I would never try to summarize the principle by a shorthand name without first describing it clearly in the same work.
And of course, the concept does not describe all the law that applies to found property, only what the common law says about a finder's priority to the chattel.
That "common law principle" applies in at least one civil law country. Meet one of the French civil code’s greatest hits, article 2276:
En fait de meubles, la possession vaut titre.
Néanmoins, celui qui a perdu ou auquel il a été volé une chose peut la revendiquer pendant trois ans à compter du jour de la perte ou du vol, contre celui dans les mains duquel il la trouve ; sauf à celui-ci son recours contre celui duquel il la tient.
Possession of movable property [= chattel] is title to that property.
However, whoever lost a thing, or someone from whom a thing was stolen, can claim it from its current holder for three years after the loss or the theft. The current holder may have recourse against the one he obtained it from.