The nutshell:
Age 17 - tested INTP, didn't fit, dismissed the theory
Early-mid 20s - tested INFP, INFJ, INTP, figured I was INFP or INFJ & didn't care enough to investigate further
Age 25 - Settled on INFP after reading Fi description & began to identify as INFP (the only type I've actually ever identified as)
I have only ever tested as an INxx ype, and I've only tested INTJ twice. I mostly test INTP or INFP now, often very close on T/F. Of course, the test is only an indicator of what you might be, so changing results does not mean a changing personality (more like changing moods and variations in the tests themselves).
The long version:
I took a test in a book of my sister's called Love Types & got INTP (the book is awful, FYI). The description did not fit well, but the Feeling ones sounded too mushy & people-focused. It made feeling sound like emotion. As a teen, I was very detached emotionally from people and did not have any characteristic empathetic NF attitude. However, the INTP description sounded too dry, cold and "scientific". I saw my inner self as passionate & artistic, just not people-focused. I dismissed the whole thing & forgot about it.
Then in my early-mid 20s I'd goof off at work and take various MBTI tests online for fun. I started testing INFP & INFJ sometimes, in addition to INTP still. The INFP & INFJ descriptions I read (I think it was on personalitypage.com) really hit home. They stirred a strong reaction in me. They made feeling sound more like people who reasoned on what is important/valuable and who were passionate about what was right/good/beautiful. That resonated with me. I didn't care enough to look into the j/p thing at that point. It just sounded like time management/decisiveness tendencies. I considered myself a decisive & willful person, but preferring unstructured environments and spontaneity.
One day, I decided to get to figure out what was the real difference between INTP, INFP & INFJ, since I tested all of these and some parts of the descriptions seemed to overlap, or I'd relate to chunks of each. I leaned towards INxP, especially INFP, because of the three, it sounded the most imaginative and creative/artistic, which I saw as some of my defining qualities. So I found my way to INFPgc and someone gave me a Ti & Fi description to read (Van Der Hoop's). The Fi description really hit home with me. I knew then I was a Fi-dominant. I began to identify as INFP. Further research just explained the other aspects (such as the j/p bit & cognitive processes) and cemented my type.