The Para magazines were made before the ban. There is no prohibition against using a pre-ban magazine in a post-ban gun. Para-Ordnance is selling the inventory of MAGAZINES they made before the ban. Their pistols are not effected by the 94 crime bill just the magazines (there is no such thing as a pre-ban Para-Ordnance pistol). You can buy a Para-Ordnance high-capacity frame that was made yesterday (Para is still making them) assemble it into a pistol and put a pre-ban high-capacity magazine in it, that is perfectly legal.
You are right some manufactures were building bunches of pre-ban receivers… but the ATF ruled after the ban went into effect the manufacture had to have the parts in stock to complete each receiver into finished pre-ban rifle for the receiver to have pre-ban status. All receivers without the necessary parts to complete the weapon when the ban when into effect were defined as post-ban. And yes the ATF did go to each manufacture and check inventory.
If I owned a Blue lable colt Match H-bar w/o Bayo lug, but with flash hider manufactured in, lets say.. 1991 or so... I can't put a tele-stock and bayo lug upper on it? Interesting.
Yes you can, the Blue Label Colt is pre-ban because it had:
1. A detachable magazine (the defining "evil feature")
2. Has a pistol grip (2nd "evil feature")
3. A threaded muzzle with flash hider. (3rd "evil feature")
(For example "evil features" = pistol grip, threaded muzzle/flash hider, folding/collapsing stock, bayonet lug, grenade launcher)
The manufacture date has nothing to do with the rifles status; the deciding factor is how the rifle was configured when the ban went into effect.
An assault weapon has been defined by the 94 crime bill as a rifle with a detachable magazine and 2 or more of the above "evil feature". So therefore the Blue Label Colt is pre ban because it was configured as an "assault weapon" before the ban.
If a rifle has a detachable magazine it can only have one additional "evil feature" before it is designated an "assault weapon". Your Blue Label Colt had a detachable magazine and 2 evil features before the ban so it was an "assault weapon" and therefore pre-ban. You can add the "tele-stock and bayo lug upper" because that rifle was in an assault weapon/pre-ban configuration when the 94 crime bill went into effect.
But if the rifle had not had the threaded muzzle/flash hider when the 94 crime bill went into effect it would not be pre-ban because it would not have been configured as an "assault weapon". It would have had a detachable magazine but only 1 additional "evil feature" the pistol grip.
You can buy a Springfield M1A now with a flash hider on it, but you cannot put a pistol grip stock on the M1A without creating a new "assault weapon".
The same for a 10/22, (it has a detachable magazine) if you put on a folding stock you would be adding 2 "evil features" (the pistol grip and the folding stock) there by creating an "assault weapon".
I hope this is a clear enough description it makes my head hurt just thinking about it.