How to correct these garbled tail numbers?
Having just N71 could be a valid tail #, but airlines almost always use all 5 characters. Most likely, the &quot;@&quot; characters are masking the actual characters in the full tail number.
A site like PlaneSpotters dot net may help, but the search on
https://www.planespotters.net/photo/search?tag=N405
gives both 405DX (Delta) and 405WN (Southwest). Further research may reveal if either of those was only active outside your target dates, but there will probably be cases where neither can be ruled out.
In this case, the current N405DX is pretty new, while N405WN first flew in 2001 (link), so that's probably it. But there could have been a different Delta jet flying in 2001 using that registration, so again, more research required to rule that out entirely. Searching Google on the full tail number is often useful that way.
Anything with three masked characters is probably beyond resolving, but with only one or two it may be possible.