Vaheguru!
There is a few subtle difference between the 2 pauriya in Aarti and Sohila Sahib. One which u have spotted. Another being in Sohila Sahib "har charan
kaval makara(n)dh lobhith mano anadhinuo mohi aahee piaasaa ||" and in Aarti "har charan
kamal makara(n)dh lobhith mano anadhino mohi aahee piaasaa ||"
The other slight difference is in Aarti "krapaa jal dhaehi naanak saari(n)g ko hoe jaa thae thaerai
naam vaasaa ||4||1||7||9||" and in Sohila Sahib "krapaa jal dhaehi naanak saari(n)g ko hoe jaa thae thaerai
naae vaasaa ||4||3||"
As to why there are some difference daas does not have any gyaan to answer but hopefully some of the blessed souls on this forum could shed some light on it