Very possibly, you're right.
There's not clear understanding of such halfround stamp.
Ok. Add year-two before 1891.
And we have the period between about 1889-1901.
I had a couple of them with that stamp and was fascinated as to why they would have done that. My explanation may or may not be correct but it makes sense to me. Thanks again manah for being the SRP historian. We can always depend on your knowledge.