I would say it's pretty normal. Individuals start shedding at different times, and males usually start before females, ewes lambing often start a bit early. Ours are being assisted by helpful jackdaws which want a bit for their nests. They usually start roo'ing over the shoulders and back, leaving the haunches til last. So you can have a mostly roo'ed sheep, with big fluffy pantaloons wandering around looking like an idiot for a couple of weeks. Or you can use hand shears on the unroo'ed bits when you do the rest.
First shear sheep often don't roo well, so may need shearing the first time, some never are roo'able.
The way to tell if it's normal or is some kind of wool slip is to see what happens when you gently pull on a small lock of fleece. Press your other hand against the sheep to brace the skin then wiggle your clump and pull at the same time. If it comes away at skin level then that implies it might be something else, perhaps as a result of illness, lambing or similar. If when you pull it, the new growth stays on the sheep, and the old wool comes away in your hand, then that is normal roo'ing. With self shedders, they may start before the weather is ideal, but they have the advantage that they still have their new season growth as a covering, unlike shearing when they can be bald in a blizzard. Just because they've started shedding, you don't have to complete the process now. You will lose some fleece, but your sheep will be warm.