My answer/comment in your original question (Action after iteration in ArcGIS ModelBuilder?) still stands, a fairly simple piece of python code will resolve this which returns a True or False value that you could use as a precondition.
An example would be:
The Calculate Value tool would be set up as:
It is simply checking that the number of feature classes in the output workspace matches the number in the input workspace.
The full python code block is this:
# Count input featureclasses
arcpy.env.workspace = inws
infcl = arcpy.ListFeatureClasses()
# Count output featureclasses
arcpy.env.workspace = outws
outfcl = arcpy.ListFeatureClasses()
if len(outfcl) == len(infcl):
In my example I am sending the buffers to the IN_MEMORY workspace, you would need to change that to where your output is going. Do that by changing the text in the expression box.