The most important factor here is nacre thickness. Many Mabe are cultured for short periods of time (4 months) to obtain the most perfect shape, but at the expense of their nacre thickness and durability.
On the other hand, there are producers that grown them for too long (over 12 months) and end up having pearls that have thick nacre, but their shapes are not standardized, and they may display one or more of the surface imperfections we discussed in the previous paragraph.
There is...