Hi I am a new member and realise this is an older topic but I would just like to add to the details. i have a similar 1900 coin and noted as per yours the 1 is slightly smaller & the tail of the 9 is shorter the overall length of the date is ten and half teeth from centre of 1 to centre last 0 whereas the normal length is 11 Thanks les Occ
I found a 1863 penny with a short serif 3 imposed derictly on a long serif 3. The New 3 can be seen clearly surrounded by the remains of the old 3 (greenish /white)as well as the end of the longer serif forming a blob. his this a known variation. I have not be able to find one