ramjet:
Yes, I looked into this with Google last year sometime, when it was rampant. At that time, there was some finger-pointing back and forth between Google and CC about it. I eventually got Google to deal with the issue, as described by the CC tech's note. It seems to have reappeared, although not as frequently. It's intermittent because like the CC tech said, the calls can pass through different intermediate or "transit" carriers, depending on cost algorithms. I now have a direct contact at Google who may be willing to fix it if you would like to help.
If so, I ask that you wait a couple of weeks, because there is a lot of high-priority work going on there now, with the Hangouts updates. Then, on a weekday morning, submit a post on the GV Help Forum. You can mention my forum nickname (For Bluescat:) in the title so I'll see it. We'll need at least 3-5 sample inbound calls placed to your GV number, which forward to your CC free (Telengy) DID number, and delivered missing or bogus CNAM. We'll need the date and times of the calls, the last 4 digits of your GV number, the last 4 digits of your CC DID, and the last 4 digits of the caller's number and if possible, their carrier (their telephone company). We need this data to be "fresh", i.e., that you collect the samples and post them immediately, on a weekday, because phone switch logs can get purged every 24 hours, making it impossible to troubleshoot.
If you can do that, the Google engineer can look at the transit carriers that were used for those calls, and fix the issue.