Tail numbers not starting with N, with domestic US carriers?
Yes, these can be legit.  For example, EI- means the aircraft is registered in Ireland.  Others look corrupt, though.  HZ-AAA is Saudi Arabia, but your HZ example looks too short.  The examples starting with four numbers don't match any country's pattern.
https://en.wikipedia.org/wiki/List_of_aircraft_registration_prefixes
The examples here that start with a string of digits all resolve to actual aircraft, if you prepend an N to them.  (Commenter Ralph J suggested this.)
Corrupt data wouldn't be too surprising.  For 2005, for example, 15000 of the 594000 entries had no tail number at all.