EnteraLite Infinity - How accurate are these things?

So my ct's mom gave me two Avent brand baby bottles that appeared to hold 260ml formula each, and I was to use both for a 6hr feed @85ml/hr, for a total of 510ml. The first night there, the formula ran out completely at 475ml, at about 5 hrs 40 minutes (give or take.) I went downstairs and mixed a bit more formula to complete the feeding. I reported it to the next nurse and heard nothing more. The next week was my second night with this client, same thing happened again. No oncoming nurse that morning so I spoke to mom about it. She said that the bottles show that it's more than enough formula, and believed the bottles to be accurate, so what she left for me was all she expected her child to be fed, no need to make more. She said I could just use the prime button to empty the rest of the formula that was left in the tubing into her stomach if I wanted to.

Up until now I was under the impression that these pumps were pretty accurate; after all, they are expensive medical devices delivering prescribed nutrition. I even have a ct. w hyperinsulinism who gets a very specific amt of D20W 24hrs/day delivered by the same make of pump. He gets glucose checks q4hrs. His safety depends on the pump's accuracy!

I spoke to my agency and they are looking into it. In the meantime, what should I trust more, a baby bottle measuring line or the Infinity?
according to Abbott the accuracy is +/- 5%....add in the prime and residual and i think you about have it.

We use the same pump for our peds patients (and mobile adults), and it's true that the accuracy is +/-5%.5% of 510mL is 25.5mL.510-25.5=484.5. So if you include your priming volume, it's reasonable that you'd have used up the whole 510mL when the pump says 475mL.However, if each bottle holds 260mL, that's a total of 520mL, which means that the pump is off by more than 5%. Is it possible to swap out pumps?