In general, if you have magnets that are not marked....
When you apply an unmarked magnet, if the pain increases, over a short time, 15min or 1/2 hr for me, then that is the North.

The South, reduces pain very quickly. I don't think "damage" happens from the North, it is just not useful for pain relief.

Magnets are very useful. I've been using them for over 10 yrs.
The new very powerful ones don't need to be on your body all day long, I have found. They correct signals, which may stay corrected all by themselves. It may be that pain is a + phenomenon, and the - pole prevents the nerve transmission signal.

As with other strong pain relief, don't over do when you feel better. Some people get over confident and over do and cause further damage. (mostly arthritics etc).

I think magnets work like Lidocaine. My experience with Lidoderm for my previously awful meralgia paresthetica, was similar. Used for 14 days in a row, and the nerve stopped acting up. Now I only get twinges, especially if I over extend that leg, to remind me of those awful days. So I think some pain can be nerves that don't turn off properly. Lidocaine is a sodium channel blocker, and sodium/potassium are the electrolytes that send nerve impulses in the nerve cell. They cross membranes and this is called generating an "action potential".

But, I am pleased for you, Stagger, that you have some relief.
Magnets can be a simple, and even elegant solution to nagging pain situations. Some pain is a signal for your attention, so don't mask "new" pains all the time, since they may need diagnosis, and don't overdo physical things when the pain is less. Moderation is the key!