Ok, so "pre-ban" referrs to parts that may be old stock, or rather a design that was around before the ban
Respectfully, except in the case of high capacity feeding devices, "Ban" status referred only to complete weapons.
If a semiautomatic rifle had a detachable high capacity feeding device, i.e., a box magazine, and also had more than one evil ugly feature (folding/collapsing stock, "prominent" pistol grip, flash suppressor, grenade launcher, bayonet lug), under the 1994 Crime Bill (which included the "Assault Weapons" ban) such a rifle was designated a "Semiautomatic Assault Weapon," or "AW" for short.
By this definition, only complete rifles could be "pre-ban," as any or all of the proscribed parts did not constitute an AW. Only the rifle could be so designated. Thus, there were no "pre-ban" lower receivers, as a lower receiver has only the proscribed pistol grip, thus by itself was not an AW.
Semiautomatic rifles with detachable high capacity feeding devices (such as the AR-15-type rifles) built after Sept 14, 1994 (and up until the ban sunset on Sept 13, 2004) could have only one dreaded evil ugly feature, and the pistol grip was it. Thus, "post-ban" AR-15 types were to be found with muzzle brakes, faux flash suppressors (e.g., the Fulton Armory "The Look"), fixed collapsible stocks (now, there's an oxymoron!), and the like. If your complete rifle was manufactured before Sept 14, 1994, you could keep your rifle configured with two or more dreaded evil ugly features, as it was grandfathered as a "pre-ban" rifle.
You can get a flavor of what a nightmare this all was, particularly for manufacturers. Want a couple hundred barrels that have to be cut down and threaded, 'cause they were made to conform to the AW ban?
Of course, all of this was pure cosmetics, as zoomie has pointed out. It was yet another harassment of gun owners and the gun industry. If the Democrat candidate is elected President, with a Democrat-controlled Congress we can expect reinstatement of "reasonable" regulations, such as the AW ban (and more, the imagination of the enemies of liberty is without bounds), though I suspect the AW ban will be written more competently to block the manufacturing of AR-15-type rifles altogether.
Regards,
Walt
PS The M14-type rifle (e.g., Fulton ARmory M14, S, Inc. M1A) could be equipped with a flash suppressor as its one dreaded evil ugly feature, as it did not have the proscribed "Prominent Pistol Grip."
PPS California bans "AWs" compoletely; New York has continued the AW ban on a state level, so "pre-ban" still applies in NYS.