Checking during a contraction vs. in a relaxed state can affect the SVE as well.
You have to get to know your docs. Some are universally generous with their exams. It pisses the patient off for you to call her 3 and the doc come in a minute later to call her 5. With those docs, I tend to be very conservative and chart to the lesser of the degree of cervical change. In other words, if they could be a "stretch to 4", I will call them three. If the provider checks after me, WOW! they are making progress. LOL. Conservative checks rarely piss the doc off. Generous ones do.
With nurses with less experience, I also see them evaluating outer rather than inner OS. That can throw off your check significantly. Make sure you go all the way through and assess the opening closest to baby's head.