Question regarding metal-bias cassette tapes.

I have been told that a portion of the data initially recorded to metal-bias tapes such as TDK-MA is permantly retained and will bleed through to any subsequent recordings degrading their fidelity. Can anyone confirm this?
No magnetic tape can be completely erased, even in a bulk erasing machine that you put the cassette into. (This is why data tapes that contain classified information cannot be declassified except by physically grinding them up). However, the residual signal is so faint that it cannot be heard except perhaps during silent periods between selections. It is less noticable than groove to groove crosstalk in a LP.

The term "bleed through" generally means the transfer of signal from one part of the tape to another part when the tape is tightly wound and stored for a long time.
I have never experienced this and I have lots of tape. I would not worry about it unless you are already having a problem with it.
...not only in metal bias tapes but in all of them...