> If you purchased a piece of land and that wasn't recorded in the registry, you are SOL because registration is what conveys title.

Sort of. The registration is what provides opposability against third parties. But between buyer and seller, the transfer of ownership happens by the contract itself. You'll have a harder time against creditors of the seller placing liens on the property, or other people claiming to be owners (e.g. if they bought the foreclosed property); how hard a time depends on the country.

And there may be still be encumbrances/claims to the property that are not subjection to registration like adverse possession or rental agreements that can be asserted against the buyer and for which the buyer's only option is to sue to the seller.