"There was a trend toward papers in the private group being slightly older, although the reasons for this are not fully understood."

Might this be due to the papers in the private group containing a higher proportion available free of charge? This point could be relatively easily tested.

Private individuals noticing problematic data might do this away from any institutional resources. Jour...

If there is sufficient data to do this without risking de-anonymisation it would be very interesting to know how the effect varies based on the publisher of the journal. This could actually be a substantial confounding effect in the analysis as different publishers are very different. It would also be interesting to know if there was a difference between OA and non-OA journals. Again, this is like...