Help With Lots Of Mysteries On This Cover Washington DC 1906

I have this cover that has been perplexing me because I know little about the U.S. cancels. Any information as well about the other oddities, would be great. There are several tiny mysteries/questions.

The cover has an untied Newfoundland #85 stamp, with a clear split ring cancel from tiny town of Barrd Islands in 1906 to the left of the stamp.

At first blush the date ("JU 29") struck me as July but it is June of course. Right?

Then it appears the cover went to Bonavista by road or boat, as on the back there is a partial "Bon" and "NEWF'D" cancel. I do not think it is an RPO--just the town. Agreed?
But what is the date? I think it is July 7.

Then there is a mysterious purple box cancel/cachet with "RECEIVED" and the date July 18, 1906. But where did this come from? St Johns? Boston? Anyone know if this is the US entry cancel?

Next, it arrives in Washington DC, but I do not know these two machine cancels: One at 3pm on July 12 with a "3" and another at 4pm at "Station G". What are these? Why would there be two? What is the little "R"?

Also, I can't make out or understand the blue pencil notation. Normally registration marks, but I'm guessing not...it looks like Sunnypol Mdse SWC?

have fun and help me unravel this...

I can't help much with the postmarks, other than to comment that Station G (back in the day) was located at the Union Building, on G Street between Sixth and Seventh Streets NW, Washington, DC.

However, as for the addressee, M.A. Winters Co. (which correctly should read M.A. Winter (no 's')), of Washington DC, consider this:

The 3p Washington DC machine cancel is from the main post office, and the cover was then dispatched to Station G for delivery, where it recieved the 4p marking. They are both International machine cancels, the the 'R' generally refers to 'received'. You will also see D and C in that die space, but in general they have no significance, since they were not used properly in a consistent manner.

Thank you. Interesting facts, as I wondered what the R stood for, and I've seen D and C before.

Cheers