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In general, the document seems to be clear and well written.  I did not find any technical issues or corrections to note.

Comments:
- The reason for using this is explained as reducing the number of ACK transmissions.  Is there a corresponding cost (e.g. slower recovery from losses) that should also be mentioned so that the tradeoffs are clear?
- The shepherd writeup mentions a Sigfox implementation.  It would be of interest to note whether compound ACKs have been found to be beneficial in practice or note any quantification of the expected benefits.  Of course these are heavily dependent on the specific LPWAN and configuration, so it would just be anecdotal data.
- There are older RFCs from the PILC working group that provide advice for subnetwork design (e.g. RFC 3819).  I was surprised not to find that cited here as a reference, as it might be important regarding tuning of configuration parameters.

Very minor comments:
- Section 4 has "Examples" (plural) in the title, however, it really only contains a single example.  It could be "Example" instead.