Yeah, this is why I never even bother trying to aspirate gastric contents on an intubated pt. I've seen several difficult NG/OG insertions on intubated pts where gastric contents were aspirated from the trachea for one reason or another (pt aspirates; one had a SBO that was literally overflowing from their stomach; etc). If you can't auscultate it, it's not in there - that's always my rule. I'm not going to bother getting a CXR on a pt to confirm placement if I can't auscultate for placement.
I've had some really tough ones where the OG (my preferred route on intubated pts) took longer to insert than the rest of the care. I usually try to get an 18 fr inserted, but sometimes you have to go smaller just to even advance it past their trachea due to the tracheal tube size. Grrrrr.
Anyway, that's why the ER is a constant learning process. The upside is, putting an NG/OG in an intubated is always a much easier learning experience than the conscious and alert pt.