I wouldn't worry about it AT all.
You know that expression that goes something like "...blah blah blah ..the LAST thing you should worry about" (or something like that). Well, your concern shouldn't even be ON the list at all (let alone, the 'last' position).
I'll tell ya' a secret -- there is NO way that they will know!
They may 'act' like they have 'special tests,' etc., (you know, to "keep you in line"), but the truth is, they don't know!
Now, granted, there ARE tests that will tell if you Shot Up Heroin, and you try to blame it on the poppy seed in Grandma Bohemia's "old-world-recipe MUFFIN," but, no, you don't have to worry about 4 vs 3 hydrocodones!
(I'm more worried about you acting all 'shifty' during your next doctor's appointment -- he'll know something is up! LOL)
Chronic pain is not predictable -- it doesn't appear every eight hours.
What's important in pain management is controlling pain -- pain docs understand this.
Telling your doc that you sometimes need 4 pills a day is not a real problem if your pain is under control -- all things relative -- and you're managing within prescribed doses.
An extra pill here and there is not against the rules. Just don't run out before the month is over. That could be considered as a sign that you're not taking them as directed.
If you ever run into a situation where pain is overwhelming, and your daily dose is not covering it, call your doctor's office for instruction.
Incidentally, some urine tests just report a yes/no answer for the presence of opiates. Others give a detailed breakdown of metabolites -- a skilled pain doc can see exactly what medication you're taking, and usually, am idea of how much once the doc gains experience of your metabolism.
These results vary with an individual's metabolism. Four pills a day is going to show different levels in your urinalysis than if I were to take four pills a day.
Worry exacerbates pain -- take a deep breath and relax. Whatever happens now is out of your control.