Random Contacts sync errors

We keep encountering Contacts sync errors. We are syncing two Macs/Lion and two iPads. There is no pattern as to where the correct contact entry was created - could by any of the four devices. We don't create on icloud.com, only use that for troubleshooting and manual repair.

I am 90% sure that all of these errors are of the form [change made to device] but [no change made to iCloud.com]. If the dbms on iCloud.com doesn't register the change it will obviously not be propagated.

Repair tip: but only if the "good contact" is on a Mac. Export the contact as a VCF to say desktop (only one works, no multiples). Then drag the "good VCF" onto the Safari/iCloud/Contacts window - slow and careful until you see the + cursor. Drop it there - audit success by watching for "Importing..." in the status bar.

Q1: Is there a way to generate a "differences report", at least pairwise - say Mac Pro vs. iCloud.com? This problem has been happening for at least a month - too long to rely on failing memories as to what changes have been made.

Q2: What about a Contacts report sorted by modification date (mod dates seem to have gone away)?

I've examined all of the Apple iCloud support articles - these are good for initial troubleshooting, but do not apply to this problem.