Double Restriction digestion of a plasmid

I'm cutting miRNA expression vector with BamHI and NheI. I did the BamHI digestion by different conditions then cut with NheI. The problem is I have unexpected bands at some conditions and the same banding patterns of the null expression vector at another condition.

My question is how can I know that the first digestion was successful? I run both the cut and in-cut plasmid alongside, but I can't see the difference! What's the expected shape on the agarose gel for the first digestion with only one enzyme and only one restriction site?