*BUMP*
Actually, the background lines are clean and very sharp and even, much like on the stamp you have identified as #5 (except it's not).
Two more points:
- The second issue typically has extremely fine dividing lines between stamps. Sometimes they all get cut off but yours have very nice margins for the issue.
- Despite the current Scott notes, the paper on the first issue is actually on the thin side and the paper on the second issue is about what we'd expect to be typical thickness, though slightly stiff.
So, based on dividing lines being present, all your stamps are from the second issue, Scott#s 4-6.