There is no single, definitive data base regarding the importation dates or dates of manufacture for Chinese M14 clones. The importation began sometime in the late 80's(probably 88/89). These rifles were effected by the 89 imported "assault weapons ban" (took effect in 1990). This ban like the 94 ban addressed the cosmetic features of the rifle.
The configuration was changed to comply with the ban and they were banned from further importation in 93 IIRC. Thus, all Chinese M14's in the USA were here before the 94 ban. Of course, not all are technically pre ban. They had to be configured as AW's prior to the 94 ban.
That means that after the 89 ban, the rifle must have been "rebuilt" with the correct type and number of domestically manufactured parts to no longer be considered an "imported assault weapon" (much the same as the AK's coming in now). Prior to the 94 ban the rifle must have legally been in an AW configuration.
Some of these rifles while imported prior to the 94 ban, were held by importers and not sold to distributors until after the ban. These can not be configured as AW's until after the 94 ban expires. Even then, as "imported AW's", they must be "rebuilt" with domestic parts to be configured as AW's. The 89 ban still applies and does not expire with the 94 ban.
One way to tell when your rifle was imported and sold is to contact the importer. Even then, it's a crap shoot. Many of the importers are no longer in business. The ATF may or may not be willing/able to trace the rifle for you. I've heard that they are obligated under the "Freedom of Information Act". I've also heard that they don't trace firearms unless the weapon is part of an on going investigation. The only other way is to have a paper trail from the original owner to you.
Another thing to consider is that nobody seems to be sure that these rifles were imported in order of serial number though it is generally accepted that low serial numbers are early imports and high serial numbers are late imports.
Incidentally, these rifles are still being imported into Canada as well as a number of other countries.
$550.00 is a great price. Stock up on U.S.G.I. parts and work to keep the AW ban from being renewed.
This is the law as I understand it, YMMV. It is your rifle after all. Do with it what you please, at your own risk.
If you want to discuss your rifle and some of the "alleged" problems with some happy owners go here;
www.battlerifles.comIf you want an "expert" opinion of Chinese M14 clones, go here and click on M14 information
www.smithenterprise.com/gen_info.htm