Yes, shedding leaves is normal.
The trick is you always want new leaves to grow and replace the older ones that are lost.
If you buy it with 4 leaves, you should try to keep it at four leaves. Hopefully good growing by you gives you 5 leaves. That's a healthy plant.
If you get it with 4 leaves and then it has three for quite some time, that is not a good sign. If they lose another leaf, it will have only two.
The happy orchid is one with good roots and it is growing a bit larger with every year. If the gradually get smaller and smaller, that is a bad sign.
Your plants look good.
