Re: "calendars such as the Tibetan or Kabbalistic"
Like most *partial* understandings, or perspectives, there are inherent truths embeded. But true question(s) should be trained on whether the truths are at the heart of the system, or structure, or are they scattered per some pattern rendered via human history and cultures. The former form is most extremely rare, while the latter covers the remainder.
One of the greatest problems I have observed with Westerners coming to follow, or trust, Eastern knowledge, is that Westerners have an enormous culture gap. This gap is so great, that the issues it brings up cannot even be adequately understood. Further, there an enormous language barriers, and barriers of historical time lapse, as well as historical accuracies. What passes for accuracy in the West, is not what passes for accuracy in the East. Is a given term placed into proper cultural and mythical context? This difficulty of doing so, with true meaning and accuracy is extraordinarily dfficult.
Most things like the calendars you've mentioned are little more than curiosities, today. The originators are dead. Only the revised versions exist (v. 1.x), and only the revised knowledge holders can interpret it.
I don't mean to hammer this issue to death, rather to illustrate the difficulties surrounding it, as the same issues arise for almost everything we study about ancient history, of any kind. Just look at how many times certain history has been revised, whether it is by means of better textual analysis, better documents found, or improvement in archeological interpretations. These are just a few things that illustrate how enormous the difficulties are.
The Kabbala is ancient wisdom from Babylon, and it wouldn't surprise me if all of these traditional forms of knowledge have a central origin, or root. From what little I know about its particulars, it contains information that spans a large number of subjects, from mythical beliefs, to practical magic, to ancient medicine.
As far as numerology, well, numbers are mere symbols. Is there magic in a symbol? Only if the symbol is an accurate map of a genuine phenomenon or territory. I've never seen any numberology that seemed to contain any intrinsic knowledge of anything, unless one stretches the meaning and outcomes to fit most any circumstances, just like we see with Nostradamus' predictions. Does this stop people from believing and whole mini-industries from popping up around them? No.
I think that the heart of any genuine knowledge here is best found by studying the subject of 'intent'. Keep that issue in mind while reading Tom's book(s); it is key.