IPL is not as effective at heating and thus killing the stem cells at the base of the hair follicle. While the IPL does damage follicles to the point that the hair is shed, eventually the follicles will re-enter their active phase and develop a new hair. Initially that hair is quite fine and colorless, but after several weeks it thickens and may develop color again.
I'm not a candidate for laser due to hair color (gray), and use thermolysis. It's slow but very effective.
You are likely to find that IPL is not a permanent solution. You laser treatments have likely killed off many of the hair follicles that were in an active growth phase. There are, unfortunately, many more that will wake up over the next few years.