Sculpt mode is not retaining my sculpting

I’m new to blender, and I’ve been trying to create a character. So far I made everything in sculpt mode except the hands(long story). I made these in another file, but once I copied it onto the main blender file and “joined” them to the body, everything I did in sculpt mode was lost. Can anyone please help me to at least figure out why this is happening?

Were you using the multiresolution modifier for both objects
If so did they have the same number of subdivisions
Did you apply the modifier

Did you join the hands to the body or the body to the hands ?

If you joined the body to the hands then the resulting object will have the modifiers of the hands, if you joined the hands to the body the resulting object will have the modifiers of the body.

You join selected objects to the active object which is the last object selected. Therefore when joining objects the selection order is important