Because these coins were issued by a king who was effectively in exile in Ireland at the time, the coins were made in Dublin and whatever circulation the coins may have seen was limited to Ireland, they are not listed in the mainstream "English/British" catalogues, but rather in the Irish catalogues. Even though they bear English designs and were intended to be substitutionary tokens for "proer" English coins. Hence, if you want to look up the coins in Spink or Krause, it's the Irish book/section you need to look up.
As for value differences, Krause lists the different months but does not list much difference in value, not in this grade anyhow. Rather, they list higher values for some of the rarer varieties, like the ones that say some variant of "8ber" instead of "Oct". Nevertheless, it is the "scarcest month", apart from March 1690, which was of course a "month" that was only nine days long.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis