Kirk - did some more testing.
The 100ANV001 folder is for "normal" MP4 videos (those not shot with the XAVC S codec, so h.264?). The files are named "MAH#####.MP4" with a corresponding .THM file.
The AVCHD file without extension actually shows as a package on the Mac - inside that is a BDMV package, containing the following folders: CLIPINF, PLAYLIST, and STREAM, along with index.bdm and MOVIEOBJ.BDM files. AVCHD videos are actually stored in the STREAM folder, named #####.MTS (I believe this corresponds to the file structure of Blu-ray discs, but am not positive).
Multiple video files of any format are numbered sequentially, with the caveat that "normal" MP4 files are numbered consecutively with photos in the DCIM folder (if I shoot a photo that is numbered DSC00032.arw, then shoot an MP4, the video will be named MAH00033.mp4). Unhelpfully, it appears that AVCHD and XAVC S files have their numbering reset on every card reformat, with XAVC S files named C####.MP4 and having a corresponding C####M01.XML file to accompany them (AVCHD resets numbering to 0, XAVC S to 1).
Folders appear to only be created as needed after a card reformat, but I have not seen any folders added beyond what I sent you.
My normal ingest copies to {yr4}/{mn0}/{day0}, naming files as {fnm4}_{h24}{min}{sec}. Neither seems to be producing any results with the XAVC S files, which end up in /default, named as in camera (C####.MP4). I just did a test with one photo, one normal MP4, one AVCHD, and one XAVC S MP4 on the card, and PM imported everything except for the THM file (which it knows to ignore) and the XAVC S file into the proper {yr4}/{mn0}/{day0} folder, including the XML file that accompanies the XAVC S file . The only thing copied to /default is the XAVC S video file. It renamed the photo and normal MP4 properly, but didn't rename anything else.
I can send you a ZIP of the card with those files if that will be helpful.