I had a question on Bava Kama 90a. I thought the concept of "kinyan pairos k'kinyan haguf dami" meant that if one person has a kinyan pairus in a field or a slave, it limits the ownership of the other person who has a kinyan haguf and does not allow him to act as the complete owner. I did not think the concept actually makes the person with the kinyan pairus into the predominant owner of the item. In fact, from the gemara on Bava Kama 89b which tries to explain that the dispute around whether the woman or man has the authority to send her slave free if he or she damages an eye or a tooth, it sounds like even according to the opinion that "kinyan pairos k'kinyan haguf dami" the man does not have the authority to send the slave free because his kinyan pairos never gives him the status of the predominant owner.

If so, why does Rashi on Bava Kama 90 a (D"H Rishon) state that the kinyan pairos of the first owner gives him the privelege of "Yom o Yomaim" even though he does not own the kinyan haguf at that time. I understand that his kinyan pairos impairs the ownership of the second owner but why should it give the first owner exclusive rights to the privelege of "Yom o Yomaim"?