If you don’t in some way save the simulation to an external format, at some point the sims will get reset. Having had play around with multiple cloth sims:-
these are my findings . . .
On the LEFT side: In this example the Shirt and Cape are 2 separate meshes each with a cloth sim. The shirt additionally has collision. The manequinn torso has collision too but is a rigged mesh with an armature and simple animation.
In the cloth panel I selected Disc cache and then Bake all dynamics:
This did the sims on BOTH pieces of cloth at the same time. At this point if you save the blender file all is fine. It saved the cache to an external folder of Blenders naming ( in the same place the Blender file exists) which came in at 19Mb. HOWEVER, I discovered that you cannot change anything about the two sims - not even rename the meshes - without the caches failing
Finally, I exported as individual pc2 files the shirt sim; the cape sim; and the Manequinn. All three of these together came in at 8Mb.
On the RIGHT, I duplicated the meshes of the torso, shirt and cape, deleted all modifiers ( including the armature on the torso) and all the sims. then added to each a Mesh Cache Modifier and assigned the related pc2 file.
In summary - export you caches if you want to keep them or have no need to resimulate ( if you’re focusing on materials or rendering say) . Whether you want to export as individual pc2/MMD or use multiple meshes together ( Alembic) is entirely up to your work flow.
Here is the Blender file. You will need to follow the steps I’ve outlined above to recalculate the cloth and save out the pc2 files if you want to see the results shown in the video above.ClothSims.blend (2.9 MB)
Hope that’s of help,