nigel, I'm not certain how to interpret SG on this point, except to say that the most common forgeries would apparently have
both perfect letters and lined-up periods/stops. I have quite an accumulation of these, but haven't given them any serious study.
Here is the excerpt for anyone who wants to see what nigel and I are discussing:

And
Scott Classic says:
"The overprint on the forgeries is clear and clean, with small periods and letters showing completely. In the genuine, letters are worn and lack many or all serifs; the periods are large and oval."
Selva, I wouldn't feel comfortable taking a guess without a big scan. Someone who has more familiarity with these than I might be able to answer based on your scans.