How are courts' official case law archives distributed and stored?
Staring around the late 18th or early 19th century, until sometime in the second half of the 20th century, private commercial published firms with a legal publication specialty regularly collected paper copies of reasoned court opinions in appellate cases from court clerks or parties to cases, retype set the opinions, and published them in bound volumes of appellate decisions, which were then sold to law firms and law libraries, usually, but not always, with editorial annotations.
For part of this time period, there were in addition or in lieu of independently operating publishing firms that published reports of appellate court decisions, officially sanctioned private publishing companies that did so on a commissioned basis by the governmental entity whose decisions were published in officially sanctioned court reporting volumes, usually with less editorial annotation.
There are reported cases going back hundreds of years before that in England and Wales, but mostly, the selection of cases that were reported was sporadic and opportunistic, rather than comprehensive.
The courts and law firms then used these report of decided cases to authoritatively identify appellate court precedents, typically by reporter name, volume, and the page upon which the court decision appeared.
Later on, other specialty commercial publications indexed instances in which one case cited to another case to facilitate determinations regarding whether old case precedents were still good law or had been overruled in part of in full, or questioned, by later cases.
The publication of court opinions in electronic form first starts to appear in the 1970s or 1980s, initially in bulk "sneaker net" media usable only by firms with mainframe computers before widespread personal computer ownership and the widespread availability of Internet access made individual court opinions in electronic form widely available on a case by case basis. Electronic form court opinion publication had become ubiquitous by sometimes around the first decade of the 21st century, with non-proprietary government sponsored neutral citation forms appearing widely five to ten years after and only becoming the majority practice in the second decade of the 21st century. The dead tree paper form court reporters continue to be published (now from electronic rather than paper originals) in almost all jurisdictions where they were historically published.
Trial court case opinions were historically not distributed at all except by interested parties obtaining copies from the court clerk or the party that served the documents upon them, and except for sporadically collected exceptional trial court rulings, this continued to be the norm until sometime in the last twenty-five years of the 20th century or the early 21st century.
would a Willesden County Court archive only have case decisions
that were issued in that facility / court division?
And how far back would they go?
There are two separate judicial branch operations to consider.
The court clerk has an official archive of case decisions only from that facility/court division/court clerk's office administrative unit, historically, in part form, then in microfiche, and now in electronic form spanning various kinds of media over the late 20th century and early 21st century as these technologies developed. I am not familiar with the record retention practices of different courts and archival indexes often note that significant subsets of records in particular places that were once kept in paper form have been destroyed by mishaps such as fires, floods, riots, building collapses, mold, paper decay, and plumbing emergencies, so in any particular location the extent of the archive's completeness varies.
There was a major effort to preserve old records on michofiche when that technology was invented, and some kinds of records were maintained on papers and in conditions better suited to document preservation than others. Of course, reporters decisions survived better since there were many copies of each one and so some editions of each volume of case reporters usually survived and some were republished from time to time.
does a court automatically receive copies of all other regional courts
of the same and higher degree of superiority's decisions periodically?
A separate operation of many courts is the maintenance of a law library for use by the judges of the court and also by law firms and lawyers and members of the public who could not afford to have their own law libraries.
This operation would typically order all of the case reporters, statutory compilations, legal treatises, and other legal authorities that the particular law library's users would need and that it could afford within its budget. Typically, regional law libraries were serviceable and sufficient but not on a par with the best university law libraries and the law libraries of the most important appellate courts. Often volumes in law libraries had to be used on the premises and could not be removed from the library room or building which was usually in or near either a court house or a university or was a part of a public library.