Might be true. Not familiar with Amiga scene but the following actions were always mostly ok in the European C64 scene, provided credit was given to original author:
* Re-using music in whole
* Re-using fonts
* SOMETIMES re-using small parts of graphics
It always was not ok and considered "stealing" to re-use complete demo routines though for example.
People did get away (reputation wise) with re-using code routines for tools, though, provided credits where given and the re-released tool somehow improved on the original.
Another thing which many people disliked for example was re-using "instruments" from music, even when melodies changed. While the players were mostly open tooling, specific instruments/sounds for those players still had to be crafted first and I witnessed a couple of conflicts when people reused the instruments.
Nothing was written in stone, though. A concept such like licenses did not exist.