Just a few meandering thoughts -

For anyone assembling a collection of exact transmission line formulae, of
which there are dozens, some more applicable to practical problems than
others, it is best to begin with the most commonly used and the most
complicated formulae. Don't incorporate approximate formulae or you will
later wish that you hadn't.

Clear your minds of superfluous Smith Charts, standing waves, reflected
power, virtual short circuits, conjugate matches, etc. A clear understanding
of how transmission lines work is essential. You should be familiar with
complex hyperbolic functions. Only metric line dimensions should be used.

What are required are calculating procedures which accepts all possible
input data and finish with preferably a single number. In some cases, if not
needed, input data can be set to zero but the facility must exist.

You will then have designed a set of step-by-step routines as in computer
programs but which can be tediously and logically worked through with a
pocket calculator. The number of intermediate variables can be large. But
there can be only one unambiguous straight-line path through subroutines.

For example, in a large number of cases the single output quantity is
related to line loss, such as insertion loss in dB, or load power in watts,
or transmission efficiency in percent, or percent of input power lost in the
line itself.

But before this can be calculated it is essential to calculate input
impedance Rin+jXin for given attenuation in dB or nepers, given phase shift
in radians and given terminating impedance Rt+jXt. Then include generator
impedance Rg+jXg and internal generator volts. Having done this you are
half-way through.

Some intermediate results may be useful. Such as input impedance which
terminates a tuner or provides a source for a receiver.

Such intermediate results as reflection coefficient magnitudes and angles
may be explicitly available but may be of no practical use. What can you do
with them? The calculation is already complete. You might find an SWR
somewhere in there if you recognise it but who cares.

Well, you get the idea. But if you had the source codings of some of my
programs I can assure you they would not be of the slightest use. You may
just as well start at the begining. There are many ways of accomplishing the
same task. A mathematical program is a work of art as much as it is a set
of logical rules. But only the programmer can fully appreciate the beauty.

First prepare a list of proposed interrelated calculating formulae or
routines.
Then write the routines on paper.
Then test them on a computer.
Then spend the next 12 months removing the bugs.
Ditto, removing the bugs caused by the debugging operations.
Then publish them in the ARRL Handbook, 2009 edition, using a better
printer.
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Reg.