OK, found what I was after regarding playing National Anthems - it's in the confidential Correspondence Guildlines which they use if you write into Bethel
https://www.jehovahs-witness.com/topic/6122134262775808/branch-correspondence-guidelines
School and Jehovah's Witnesses (1983), page 29, paragraph 2
Class Instruction - Music and Art Instruction
Even during practice sessions, Witness students would not share in playing national anthems or songs connected with religious or national holidays.
Branch Correspondence Guildlines, page 57, paragraph 4
Flag Salute and Anthems
If a person in a band or an orchestra participated in playing a national anthem in a patriotic ceremony, he would thus be expressing total agreement and making an essential contribution to the patriotic act. A Christian could not do this and remain in good standing in the congregation. In contrast, if music instruction in school required a student to show that he could play a certain anthem, not as part of a ceremony, but merely as a demonstration of musical skill to the instructor, this would be a matter for personal decision.