Curious Abbreviations on Probate Records

I work with probate records quite a bit. Mostly by choice because I love probate records so much. It's doesn't take much prodding to get me to go to the probate court to do research.

I have noticed some abbreviations written on the outside of original documents and I've been curious about what they mean. I started some dialog about this yesterday on my Google+ wall. My quest has taken me on a journey greater than I had expected. I still haven't found an exact answer yet but I'm getting closer.

Here are the abbreviations in question: C., C.R. and R.  They appear on the outside of will or administration file documents and I would like to know what they mean.  Here's an image to show you exactly what I mean:

Then I found a document that had typed out indicators : Filed, Returnable and Allowed. Perhaps the R. refers to the instrument (document) being returned? Notice the abbreviated R. appearing again below the form text.

Next I found another document with an extended abbreviation - Cet. Ret. - which I am guessing is a longer form of C.R.

Perhaps C.R. and Cet. Ret. stand for Certificate Returned. That is my current guess. If you have the definitive answer to this mystery please feel free to comment. I feel like I am getting pretty good at interpreting probate documents but these abbreviations are still tripping me up.