'telo LI anpa'
I agree that this seems very odd, since we use two different words and here we have only one, which appears to mean "then" in two different senses. But 'la' actually means something more like "under these [just given] conditions", which is much vaguer. Indeed, the distinction between "if" and "when" in English is often just as you imply -- something about the certainty of the antecedent occurring. In fact, we often correct the one with the other, to indicate a degree of confidence . That distinction, however, is not relevant to 'la', which is rather what is left over when that distinction is dropped, something closer to the logicians' "if...then...", where all that counts is the actual truth of the components and everything is fine so long as we don't have both the antecedent true and the consequent false.