The pileup mixing seems to throw away all the digis that are coming from the mixed pileup. This makes it difficult to add the digi markers.
The digi collection does not exactly contain the same pixels as the cluster collection. Mostly the digis is a bigger set (with all the cluster pixels available in it), but for now on I create a lookup table and add zero markers for any extra cluster digis that might turn up. The rate of "mocked digis" is a good number to pay attention to when running the simulations even on the grid.
TODOs
Add modifications to the pileup mixing modules so that it propagates the digi flag collection from the mixed data and it can be combined to a correct flag collection