For machineguns, the 'magic date' is 5/19/86. Any machinegun registered on or before that date (except imported dealer sample guns) is transferrable to any individual, depending on local and state laws, of course.
Pre-86 dealer samples are transferrable to any special occupational taxpayer (SOT) and may be retained by the SOT after giving up their SOT status.
Post-86 machineguns are transferrable only to government agencies, for export, or to SOT's with a police demonstration requestion letter, and may not be retained by the SOT after giving up their SOT status.
The 1994 AW ban only affects SEMI-automatic weapons, and then only governs the cosmetic features a grandfathered pre-ban weapon is allowed to have, versus what a post-ban may have. Machine guns are not semi-automatic, so are not covered by the 94 AW ban.
Short-barrel rifles and short-barrel shotguns which are semi-automatic are covered by both the NFA restrictions (tax, transfer registration, etc) and the cosmetic feature restrictions of the 94 AW ban.