Red Bull clinched its sixth constructors' title with six races to spare in Japan, which is another entry for the Milton Keynes squad into the series' record book that it has been steadily rewriting this year.
Team principal Horner conceded that losing its streak of consecutive race wins in Singapore was inevitable.
And while the carrot of an invincible season is no longer dangling in front of his team, Horner says it must continue "pushing the boundaries" as its current success will be hard to replicate.
"I think a repeated season like this is, you know, it's a golden moment for the team," he said.
"To do better than we're doing I think it's impossible. So, I think we're riding a wave and of course we want to try and ride that wave as long as we can.
"But Formula 1 is a fast-moving business. You see how quickly teams move up, move down and Singapore if nothing else demonstrates that there can be zero complacency, that we have to keep pushing the boundaries."
Horner also paid tribute to the crew members that produced such a dominant RB19, which displayed almost no weaknesses and in the hands of series dominator Max Verstappen sat at the top of the pile across all speed ranges.
"Last year was a very strong year for us," he added.
Source: Autosport