Because they were all done by hand some embossed stamps are more clearly defined than others. It is possible that someone has re-drawn that edge... a closer scan would assist you and anyone having an opinion. Scan the back as well as there may be a little bleed-thru if a pen has been used on the front...again, a closer scan would assist

The above shows a typical edge of the 10p embossed issue which shows some lack of detail so perhaps your stamp was particularly bad and the owner decided to re-draw? Being a three margin stamp worth a lot less than a four margin it might have seemed to improve the look but only a close look at it would "decide" if it has, indeed, been re-drawn.