.al files are usually missing when a perl module isn't correctly installed

Actually, in my experience, it is much, much more likely that the reason that a *.al file is "missing" is because the module in question doesn't actually have (in this case) a setup_drive(r) method.

Searching for when DBI may have acquired a /^setup_drive/ method, I only found:

Changes in DBI 1.35, 7th March 2003
 * Added note to install_method docs about setup_driver() method.

Looking at DBI.pm, I see that it does not use AutoLoader or such and so there is absolutely no point in having an AUTOLOAD that looks for *.al files when a method in DBI is not found.

A big part of the problem is this line:

@ISA = qw(Exporter DynaLoader);
[download]

It was a pretty stupid idea to use inheritance in the design of Exporter and DynaLoader. One or both of those likely similarly use inheritance to make use of AutoLoader. Inheritance in transitive so this all makes DBI also use AutoLoader even though it had no intention of doing so.

It is a bit of a mystery why DBI's inherited AUTOLOAD can be found but not "sub setup_driver" which is plainly visible in the latest DBI.pm and has been in that module for several years. But the "missing *.al file" is a complete red herring.