the realization for passing theses values at run time through an internal stack

Don't confuse implementation (perl) with the language (Perl)! Otherwise, you'd have to start claiming Perl has pointers!

perl -e 'print scalar ($a++,"b","c"), $a'

Following your explanation one might think that $a should never be incremented, since the "list" (the stack) is never built!

Bollocks! What you have here is the scalar comma operator. From perlop:

Binary "," is the comma operator. In scalar context it evaluates its left argument, throws that value away, then evaluates its right argument and returns that value. This is just like C’s comma operator.