This is a nice spoon.
Maybe a naive suggestion, but :
since the doe-paw or hoof design of the handle is quite specific, a comparison with possible comparable model(s) published in reference books may be provide interesting clue regarding the origin of the spoon.
You say it is determined but I would say the mark possibly of..... and with a question mark.
Andries Sjoukes, registered in Franeker 1647-1675.
Andries Sjoukes, was born around 1622 in Dronrijp; worked between 1647 and 1675; occupation goldsmith. Married in Dronrijp: 1st in 1647 to Dorothea Maghalis; 2nd in 1671 to Wietske Thomas. Buried in Dronrijp in 1675. Mastermark AS in round frame https://en.wikipedia.org/wiki/Dronryp
However It could also be AI in a round frame for Agge Jelles Reinalda, see Voet # 404, registered in Franeker.
Agge Jelles Reinalda was born in Dronrijp around 1630 and became a citizen of Franeker on 16 June 1657, silversmith by profession, died before 29 October 1691.
Agge Jelles Reinalda was apprenticed to the Leeuwarden silversmith Jan Douwes in 1638 and will have become a master silversmith before 1653, since he had a mortgage debt as a silversmith in this year and is mentioned as such.
His work includes the communion silver from Franeker (a cup with the date letter I for 1660, two dishes with the date letter N for 1664 and a dish with the date letter Q for 1667) and the communion cup from Dongjum with the date letter P for 1666. See: Voet no. 186; Cat. the Exhibition of Frisian Silver (1927) nos. 145, 216.
The mark on your spoon, is it; AS or AI or CL conjoined or...?
The mark of Andries Sjoukes, Zilverstudie Jan Schipper 2010
The letter(s) in the master's mark are not clear to me and I cannot link it with certainty to a specific Frisian master silversmith.