You're coming at it from the wrong direction if you're trying to build an internally consistent model that will predict which pagan practices a religious group will embrace and which they'll shun if you're going to actually look at the pagan origins and doctrines surrounding the individual practices. Those don't matter. The "pagan origins" concept only comes into play after something is decided to be banned as a justification. The best example I can think of here is with JWs not celebrating holidays. They don't celebrate christmas, halloween, easter, or valentines day because they have pagan origins. But what about thanksgiving? They clearly can't claim pagan origins there - it was started by a bunch of christians recently enough that its origin can't really be disputed reasonably (of course it's got a dark past to it that's often glossed over in schools, but that's beside the point). But nonetheless JWs don't celebrate thanksgiving...the justification being some wishy-washy condemnation over holidays that encourage national pride or some such nonsense. I don't know if it's the official JW line on the topic but I was also always told that we didn't celebrate mother's/father's day because doing so might imply that we don't need to "honor your father and mother" on a daily basis (obviously that's nonsense). Another counterpoint - Anniversaries. These are celebrated by all JWs that I ever knew. These can be said to have pagan origins from astrology that ascribe special significance to the particular time of year that some event occurred. And certainly we wouldn't want to risk implying that we should only love our spouse one day a year! But anniversary celebrations are fine...it's all confusing if you look at it from this perspective.
Instead, look at things from another perspective - what holidays/events are commonly used as talking points among acquaintances due to their near-universality in the culture, and what ones might lead to invites to a group celebration with non-JWs? In short, what things might risk leading to a closer connection between non-JWs and JWs? It's Christmas, easter, thanksgiving, halloween, mother's/father's day, valentine's day, etc. It's certainly not wedding anniversaries because unless you tell someone when yours is, they're unlikely to bring it up, and even if there's a group celebration of an anniversary, they're usually relatively private affairs so there's little risk of someone from work inviting you to theirs or a JW inviting a non-JW to theirs. If you do a half-way decent job of separating a JW from broader society, there's no risk of a wedding anniversary (or, say, a graduation party) being the impetus behind a JW finding camaraderie with a non-JW. Contrast those with birthdays and you'll see why one annual, self-aggrandizing event is no good and anniversaries and graduation parties are fine. Birthdays often become known to your casual acquaintances and sometimes just by dint of you being a decent person such ones will take it upon themselves to celebrate your birthday (especially in the formative years of youth) or commonly there are group celebrations at work for everyone whose birthday falls in a particular month or quarter.
I would conservatively estimate that the real reason 80-90% of the policies/doctrine in place in the JW faith are there for purposes of either control of adherents or to separate them from society. When you start to look at it from that perspective, reasons for the inconsistencies between the application of justifications like "pagan origins" or "we are no part of the world" start to become clear.