I think this is actually the most common experience. The data I've seen says that scores on all four 'axes' are normally distributed. So it's actually fairly exceptional to have strong, predictable positions for every letter; cutting a bunch of normal distributions down the middle means most of us are on a boundary.
And yes, it's probably those silly E folks saying they never change. God forbid we wake up tomorrow testing as E, we'll have a paradox on our hands.
The folks who have argued that point with me over the years all happened to be strong E. I'm talking perhaps 3-4 people over 20 years - not a huge number to go on, but it was the only consistent I saw (male/female/old/young/etc).
Me: "Wow, I took this a few years ago and was a moderate F, but now I'm a slight T".
Them: "That's just not possible. It doesn't work that way. You just don't remember what you had before. It doesn't change".
Me: "WTF??"
Amazingly, I've had arguments about this with folks. (probably E folks). They claimed that "it never changes", which is just patently untrue. Perhaps E folks don't introspect enough to re-evaluate their views on things? I know I tested different 5 years ago compared to when I took it 20 years ago.
I don't really see how you couldn't retest at least somewhat differently.