The fact that something worked does not prove it was repeatable.

Working once and working reliably are very different claims. A single success can come from skill, from favourable conditions, from a detail nobody noticed, or from nothing at all, and you cannot tell which from one instance. Repeatability is a separate question that only repetition can answer.

Before building something on top of a method that worked, run it again in slightly different conditions and see what survives. If you cannot test it, at least write down what you think made it work, so you can find out later whether you were right.