You should use the Part VIII column (b) amounts from the previous year return. 

The part IV column (c) has the amounts from the prior year before that return, which doesn't include the current year losses, or losses allocated from dispositions of other activities.

That's not quite correct.  The part IV Column (e) might be the same as part VIII column (b), but not always, so that isn't where you should look when carrying forward amounts to the next year. 

Specifically, it doesn't include other passive trade or business activities that they may have in Part V, and it doesn't have any allocations from properties that were disposed of that year that may have had left over losses that were allocated to the other passive activities.

You should instead use the Part VIII column (b) amounts from the previous year return to carry forward to the next year return.  

Great input. I updated the answer.