I used a couple of 0C Kodak safelight (standard 5.5") for years, until I took John Wimberley's darkroom workshop. He's ADAMANT about stray light in his darkroom and preventing any fogging whatsoever of highlights. He tested the OC filters, and they failed.
I've tested my 0C filters and they passed. This is the bottom line about the absolute need for testing - it accounts for other variables.