Here's what I think, put into a larger context.
Everyone knows that Ragnar is mostly fictional. If there's a real person hidden in all the stories, it's a Ragnar who was father (only) of the leaders of the Great Heathen Army.
Later generations tried to capitalize on Ragnar's fame by faking descents from him. We see a lot of that, and we've struggled with pieces of it on Geni for quite a while.
One of those fakes -- I think -- is the idea that two different Ivarrs are the same person. Irish Ivarr is not the same as Ivarr the Boneless, but the descendants of Irish Ivarr tried to make it look like they were the same.
In the original story of Ivarr the Boneless, he was impotent and had no children. That was an embarrassment. Not just to the Irish folks who were claiming descent from him, but also to everyone else who traced their line to his father Ragnar and had to be related to a man whose masculinity could be questioned.
So, the later sagas try to spin a different story. And, some modern historians are still falling for it.
It's all very romantic, but also transparently false.
The current dates are probably the best available.
ivarr the Boneless disappears from English records after 870. The Anglo-Saxon chronicler Æthelweard records his death as 870.
The Annals of Ulster describe the death of a man named Ivarr (Ímar) in 873, but he was probably a different person.
It would be easily possible to play around with his birth date, but we'd have to re-visit the chronology of this entire section of the tree. With a father who might be fictitious and no firm dates in the primary sources anything we choose would be a bald guess.
I could support blanking the birth date, or changing it to a very broad range (on the order of, say, 760 to 850) but not just fussing with it.