Why most of my cloth cc's weight paint is gone when exported

I created a cloth cc.

I imported it S4S

and then exported it again.

Before it was imported, the weight is there (yellow color), for example for the L_Clavice. ( Ihave used weight paint transfer process)
But then after imported and exported again, the paint is gone. Only a few left.

Why?

Did I imported it incorrectly?

I have a long dress.

By using the sims nude model, I  import my dress.

The nude model only have 1 mesh group, which the top area.

My dress is almost up to the feet. 

Using the same cut number from the nude mesh group, I imported my dress.

Is it wrong?

Do I have to find a model with mesh group that also up to the feet?

I'm sure I still have missing puzzles here.

Help.