Forgeries appear to be common among this issue. Crude forgeries are easy to spot. I believe these are forgeries but am unable to find examples of forgeries that have some of the same details found on them. Does anyone know of an online reference with images of known forgeries of this issue?
Thank you for your response. Vasia's examples were extremely helpful when first trying to determine whether these were forgeries. Examples found elsewhere varied in appearance. Some were as crude as the stamp in the OP. Others appeared to have finer detail yet classified as forgeries.
I have blocks of 25 for each value of this issue. Reviewing them reveals variations by position number. IMO variations in the appearance of forgery examples found online may be due to variations by plate position number. Lack of detail, as you suggest, is the best measure when attempting to decide whether a stamp is genuine.