Digital OPK Question

Z
Sorry in advance for the lengthy post, hoping somebody can help me. I am using OPK's for the second month in a row. They are the digital clear blue easy kind and last month when I ejected the stick, you could really tell the progression. This month, it's not the case. I'm on CD16 and only have one line when I eject. (I started CD8 and at that time DID have a second line, by the way). ANYWAY, still no smiley. Last month I got smiley on CD18 but again, I saw the two lines get darker. I know you're not supposed to pay attention to that with a digital, but because I DID see it last month, just wondering what the deal is. Any thoughts? Thanks in advance!