I went to the Howes website, but didn't see any info listed about overtreatment. I know Stabil states on their website that overtreatment is okay. My recommendation is drop Howes an email and ask them.
STA-BIL® Diesel All-Season is an advanced all year formula for all your diesel additive needs. It cleans and lubricates fuel injectors, provides anti-gel protection down to -40 degrees Fahrenheit and also boosts cetane. This product is safe for all diesel engines and it comes packaged in an easy pour, non-slip, 20-ounce bottle that treats up to 150 gallons of fuel.
USAGE DIRECTIONS:
Pour contents of bottle into tank before fill-up to aid mixing with fuel.
Over treatment, use of entire bottle or more frequent use is safe and will not harm engine.
Promptly clean up spills from vehicle finish. Do not use in gasoline engines.