There is a debate whether a convert can marry a mamzer. Why can a shetuki (unknown father) and asufi (unknown parents – abandoned child)not marry a regular Jew? According to the gemara, by Torah law they can, but the rabbis wanted to institute a higher standard for yochasin, lineage matters. The gemara discusses in the asufi case distinctions between ways the baby/child was abandoned. Not in every situation is it considered an asufi.