First edition first volume was a much smaller print run than subsequent volumes.
So if I bought the first day it was available, that’s not necessarily first edition?
In the UK, it probably is. But it was relatively unknown at the time, so it would be surprising if you had.
First edition first printing of Harry Potter 1 from the UK was only 500 copies in hardback. That one fetched a recent record of 190.000 dollars. Paperback is expensive as well, from ranges between 2k and 10k.