Harris Polls 1980 Reagan / Carter
January 36/59
February 32/64
March 40/58
April* 48/45
May* 42/33
June* 51/44
July* 61/33
August* 48/28
September* 41/37
October 9* 43/39
October 22* 42/39
October 27* 45/42
November 2* 45/40
November 4*
(Election Day) 46/41
*Reagan Leading
As you can see Reagan’s lead held steadily from April onward. I don’t know what other polls like NYT or Roper had.