Flight 628, what plane used on a specific date
 

At the risk of looking like a geek, what N number was used for AS 628 SEA-JFK on February 28, 2020? Was it N275AK?

Yes, according to flight radar. I'm sure bigger geeks than I have better sources.

It was N275AK.

This is just baby geek level. You are on your way :)

Neil

Well now I'm curious...why has it been at JFK for 2 weeks?

It hasn't, you can view the Activity Log:

https://flightaware.com/live/flight/...ageActivityLog

D'oh! I was just looking at the linked track for that particular day and wasn't realizing that it was only that particular flight.

For my historical flight tracking on my.flightar24 & flightmemory, which I've tracked down back to 2001 - I've looked up just about every tail number I've flown on!
There's a few tail number that just seem to be lost to any records - I've tried both free & paid services. I found flightstats to have generally the best paid archives just FYI :)

But if you're looking for domestic US flight info on aircraft type, tail #, or flight timing, Bureau of Transportation Statistics (BTS) keeps good historical records: https://www.transtats.bts.gov/ONTIME/

The search interface is a little clunky, but some guy made simplified interface that searches the same DB which you can find here: Aircraft Tail Number Lookup