My original install with my TiVo cable card went surprisingly easy (way back in 2010). When I upgraded my TiVo to a Roamio (6 tuner 3 TB version), all I did was pop in the old cable card and it worked fine. I've never had any issues. I've heard CC knowledge in the field is dropping as a buddy had varying issues when he had a suspected bad Bolt. Diagnostics kept pointing to the TiVo or the card, and VZ would bring out cards that were suspect, and if one didn't work, it just went back into a box full of used cards. Eventually, I think it was the TiVo, I'm hazy on the final resolution (it was successful), but ultimately VZ kept working at it until it was fixed. There was a possible issue with the ONT, too, which was replaced.Congrats!
Not that this will make you feel any better, but I don't remember ever having a successful cableco install with my TiVos (from either Comcast Xfinity or Verizon Fios). They never seem to be able to pair it properly upon installation and I have to spend hours on the phone with them after the fact. That is why I dread losing my cableCARD pairing and why I have a backup of the hard drive with the settings I need, ready to plug in the moment I have a problem.
Anyway, I'm just pointing out that the part that was the most challenging for you is not limited to Charter Spectrum. I'm not sure about Spectrum, but both Xfinity and Fios have an on-line tool to activate cableCARDs and that has never worked for me either. I wish it was an easier process, but then, the cablecos would have to WANT there to be!