Are Teachings developed "after the fact"? This might be a poor question, for which I apologize but I am trying to gain some insight on this idea I have had for a long time... It seems that paths and practices are taught to people with the intent that they have the same results that the teacher did by doing that. But the teacher might have come across the practice by accident, and the teaching is simply their experience, not a principle. 

When I read suttas, interviews, articles, different sects' explanations and so on, there is an almost infinite variety of statements and interpretations, and people seem to get lost in words. If a practice was really "true" absolutely, then there could be no difference of explanation or understanding, right? It certainly is not like Physics, where everyone would get the same results of a clear experiment.

If a Teacher was so wise that they came up with the practice before they had used it, that would be a miracle indeed. Is it not the case that all that is taught about spiritual development is basically experiential? Even the Buddha had to learn by doing. We are just following what he said.
... It seems that paths and practices are taught to people with the intent that they have the same results that the teacher did by doing that. But the teacher might have come across the practice by accident, and the teaching is simply their experience, not a principle.
When I read suttas, interviews, articles, different sects' explanations and so on, there is an almost infinite variety of statements and interpretations, and people seem to get lost in words. If a practice was really &quot;true&quot; absolutely, then there could be no difference of explanation or understanding, right? It certainly is not like Physics, where everyone would get the same results of a clear experiment.

If you as about a long path, then the land marks different people describe about the path would be different. Thus there are many description of the same road but different land marks. E.g. The middle path is described within these two Suttas abide the different landmarks. Samma,ditthi Sutta, (Ekā,dasaka) Cetanā’karaṇīya Sutta. Also by nature of the practitioner certain landmarks on the road would be of more significance than others. This will result in different descriptions. Also Buddha having the ability to discern what would register in the mind of the practitioner, gave most appropriate &quot;directions and land marks&quot;.
Another this there are multiple variations and techniques which give certain spiritual or &quot;out of the world&quot; experiences which the practitioner may mistake to have achived the final goal or mistakenly believe is the path when in fact it does not take you to the final goal. (Somewhat related is Brahma,jala Sutta also as introduction on it which highlights how wrong view arise.) Since you have some uncommon experience you hold that the method and techniques you practised has got you or will get you to the final goal. This give arise to different descriptions and variation and debates about the technique.
Some times these variation can be from people who have gone to the final goal. Some people have had only some imperfections or uncommon imperfections and would have done a practice to remedy that. Having achived the final goal he would teach from his experience which would result in an uncommon description of the method, which might not always work for everyone.

If a Teacher was so wise that they came up with the practice before they had used it, that would be a miracle indeed. Is it not the case that all that is taught about spiritual development is basically experiential? Even the Buddha had to learn by doing. We are just following what he said.

The Buddha as well as many disciples had to do countless lifetimes of experimentation before crossing. So the part descried with what worked out the countless techniques that have been tried and tested.
Even with imperfect techniques which that you to an intermediate station, you need some experience which you describe and when the students practice it and gain some experience they believe. So some experience which can be replicated by a practice is the for runner of teaching a successful meditation technique.