Were his foreign royalties always higher than whatever it was Martin paid him[...]?
During his lifetime, yes.
Martin paid him, about $10,000 every two weeks by the early 1990s...
Bukowski was
earning more than that from foreign royalties ten years earlier, in 1982 (adjusted for inflation).
And we might take Martin's $20,000 a month claim with a grain of salt, since in 1992 Bukowski said he was earning $7000 a month from Black Sparrow royalties. Unless that amount tripled over the next year or two, Bukowski never saw $20,000 a month from Black Sparrow.
Linda
may have seen that amount eventually, but then shortly before he sold the Bukowski rights to HarperCollins, Martin characterized Bukowski royalties as "pennies":
Clearly they weren't literal "pennies," or HarperCollins wouldn't have paid what they did for the rights (they also bought the rights to Bowles and Fante Black Sparrow titles in the same deal, which, as I recall, was a little less than $2 million). In any event, and whatever the amounts were, by the time Black Sparrow started to make any significant money for Bukowski, he was near the end of his life. So he benefited - during his lifetime - much more from foreign royalties.
Look at it this way, when Bukowski bought his house in 1978, he made a 50% down payment (either $40,000 or $60,000 depending on which source you believe), then doubled his monthly mortgage payment so he could own the house quickly. In 1979 he bought a new BMW for $16,000 cash. At the time those things were happening, he was earning $500 a month from Black Sparrow.