FWIW. Using the boot code with specifics, e.g., tz=PST+8PDT,M3.2.0/2,M11.1.0/2
is not only much much smaller, it empowers the user to change when needed the Daylight Savings offset.
Using the tzdata means if the DST offset is changed, the user will either have to create/update their corresponding data file, or, worse wait for an update from the extension maker. zic comes to mind!
That is two benefits of using the default, i.e., avoiding the extension.
It is understandable if a user is located which is not well served by TZ specifics, although I can't think of any.
But as with most things tinycore it is your decision on what works best for you.
Glad to hear that you have it working.