Many thanks for showing more of this collection! There's some really amazing items here.
There are questions in my mind that I hope the owner might want to consider and research to add to the writeup.
One is the 2c added to wrappers both in the first post:http://goscf.com/t/77952
and here on page 2 and page 8. The 10c green added to the registered wrapper here I believe represents 8c for the registration fee plus 2c for something else. We are hampered by not knowing what the contents were, but there is a 2c rate for mailing samples of merchandise, that had to be in an envelope or wrapped separately so it could be inspected. Further, the page 8 wrapper with a 2c stamp cannot be a postage due usage. The 2c cancel and the one on the wrapper match exactly so the stamp was added at time of mailing. The blue crayon marking could use some explanation from a Hungarian collector.
The wrapper on page 3 uprated with a 5c stamp is not exactly for additional weight. 1c took care of up to 2kg(!) of printed matter, plus there were upper limits for size and weight of printed matter. But I suspect that 5c would be either for added commercial paper or just a letter included with the printed matter item(s). This usage might be guessed at by how large the packet was originally.
I believe that the page 6 Hungarian due cover story needs revision. The "T" marking is likely Hungarian even though New York had the marking; the style been commonly used around the world. Austria-Hungary was a UPU member so there shouldn't have been postage due charged unless perhaps contraband merchandise was found upon inspection.
Page 3 notes no date in the originating cancels, but on later pages it is noted that this is normal, which it is for wrappers.
The Guatemala cover uprated 20c is wild. I have no guess what that represents but others will wonder also.
I hope that John Becker can correct me if necessary or provide some or all of the answers.