You're probably going through what newbies do (myself included)....your measuring style is so inconsistent that you think you're gaining or not cuz of how hard your pushing into yourself. BP and NBP gains have to be somewhat the same, unless u gain a tone of weight and such, but it's all length, just if u wanna include or cut the fat/skin there. Either way just be consistent with the way u measure, I know it's hard as sometimes (in the past moreso) I'm close to wllling an 8th inch by practically cutting into myself with the ruler I'm pressing so hard which I don't recommend. For bone pressed a real firm press but not where it causes pain is what I go by (but still to the pelvic bone area), and for non-bone press u still lodge right into where your penis meets your body but no press into the soft tissue, etc....this has helped me as I was a classic case of inaccurate measuring to fulfill my mood (if I was down I'd swear I shrank or if I was up or desperate lol, I'd swear I grew when in reality I was only pushing harder from about the 3 days previous haha)
As u can see I've learned a lot, do yourself a favor and don't let the ruler rule you and your ultimate goal. Only measure once every two weeks, I've pushed it to 4 weeks myself, and it's a lot more healthy (mind and body) and I'm starting to really gain from it. Best of luck.