In my circle of tube usage, we always speak of tube bases like "6BA6
and 6AU6 both have the 7BK basing". Then I look in my oldish ARRL
handbooks, find the chart of tube bases and see the 7BK pinout.

Many of the tube databases on the net use the same terminology for
bases.

Obviously for the number-letter or number-letter-letter bases the
number is how many terminations. And the letters seem to have been
assigned sequentially (or maybe not?)

And there are some oddball bases (power tubes etc.) that don't follow
the number-letter pattern but instead are simply numbers.

Is the ARRL handbook the "final authority" on tube basing, or (more
likely) is this simply an excerpt from a more authoritative list
somewhere else?

Tim.