10.12.3 Combo update failing code sign verification, certificates fail, and mysterious error message from the Mac Store

Apple Care was totally stumped by this problem and I'm not sure where else I'd be able to verify this sort of information.. I'm hoping someone here can help provide some sort of an explanation so I can lower my threat level back to elevated.

I ran codesign -vvv on my download package of macOS Sierra 10.12.3 Combo which returned ".../macosupdcombo10.12.3.dmg: code object is not signed at all"

I immediately reached for the nearest tin foil hat andx proceeded to check it with the only app in the Mac store that verifies code and certificates RB App Checker Lite (side note: it works very well, more people should be using these kinds of assurances). It returned a longer list of issues than I've ever seen before.

I went back to download it again and some other various updates from the support.apple.com/downloads website the same place I just had downloaded the one above from a few minutes before and was given this error message after the website slowed to a craw land only loaded the page's header:

I spoke with Apple Care over the phone about all of this and was not given any sort of assistance at all and it seemed like the woman who helped me didn't believe I actually got this from their website. She asked how I did it because we were in a screen sharing session at the time and she could see it was a real webpage linking to Apple which I'm not noticing is cut off from my screenshot.

I tried again 2 later to determine if it was safe to install the software that I just downloaded but 2 hours into me being routed along the chain of command I was transferred to a supervisor who suggested there had been some sort of testing done when in fact there was nothing of the sort, not even a sysdiagnose command in the terminal and I had to even tell them what that is... So now I am still concerned for the authenticity of this update I downloaded from one of the only two official sources, disapointed in their lack of interest in assisting what seems like a potential security issue, and pretty surprised to find out that such attitudes exist.

Can anyone shed some light on all this?

The session was ended abruptly which almost didn't seem like legitimate Apple Care behavior and I realize by this point after two hours of typing I could have been a little more understanding of the limitations of his understanding of the operating system but I've never encounctered less than friendly Apple employees. I'm wondering could this have been a faked chat/download/website??