Zariel (LE Archduchess of Avernus in Hell) was once an Angel (a LG Solar). As were all the Erinyes Devils. Every single one of them. They're all former Angels who are now Evil.
Inherently good creatures (literally comprised of the essence of Good), raised in Good places (literally in Heaven, at the service and in the presence and under the guidance of the Gods of Good) who changed alignment to Evil.
Are you saying they can fall, but Orcs cant be redeemed?
Which goes back to how they were created. Good generally values freedom of will, evil does not. But more to the point these are specific exceptions spelled out in the MM, there is no corollary for orcs.
I will say this. I can see why some people might think there are exceptions to the "orcs are evil" rule. Let's say for a moment there is. But what would the consequence be? Assume for a moment that orcs are evil by nature (which I believe the MM says). So let's say a small percentage are not evil.
How many? Well this would be effectively deviant behavior so let's say they're the equivalent of a sociopath. About 1% of people today are considered sociopaths. While 25% of the prison population are sociopaths, many sociopaths just deal with their lack of empathy and are productive members of society. Others are Hannibal Lecter.
So if similar numbers applied to orcs (again, just a thought experiment) then 1% of orcs are not evil. But while the majority of them may not be driven by an insatiable hunger for slaughter, most are probably just going to go along with it as a matter of survival.
So let's guesstimate that 25% of the 1% buck the trend. Well then somehow they still need to escape, find a new home and so on.
But if they escape they find a hostile world. After all every orc anyone has ever met was an enemy.
Could it happen? I've decided that in my campaign it's effectively 0.
So orcs in my world are effectively all evil. The odds of running across an orc that is not evil is so small it doesn't matter. It may be different in your campaign.
Beyond that I don't see a reason to continue this conversation.