[accrual]

Yep! There is very real concern about accidentally introducing Earth life on others moons and planets, and then "discovering" the introduced life instead of actual native life.

As you mentioned with tardigrades, there are life forms and bacteria that could possibly survive a long duration flight through the vacuum of space, then proliferate once it reaches the surface somewhere.

This is usually guarded against by various sterilization techniques applied to the spacecraft before launch, and there is a discipline dedicated to ensuring these events don't happen:

https://en.wikipedia.org/wiki/Planetary_protection