I met a bloke once who was absolutely obsessed with whatever his Myers-Briggs personality type was, like it was The Word and The Last Word at that.

I think any of these things, horoscopes, tarot cards, runes, tea leaves, Myers Briggs, can give us insights to explore and tease out whatever is already preoccupying us and they are valuable as a lens on any given situation.

But I would not give any special credence to Myers-Briggs, not least for the reason you've already noticed: you did it four years ago and got one result and now you've done it again and have a different result.

There's an interesting Wikipedia article about Myers-Briggs and the ideas of Carl Jung which informed it. Wikipedia is one starting place for exploring these ideas and has lots of references that you can follow up, but as with Myers-Briggs, it's a good idea to approach Wikipedia with a healthy dose of skepticism.