I am not a native English speaker, a reason for which I struggle to understand the meaning of some sentences used in literature which have even slightly different structure than ordinary. I quote here a sentence from 'The Eye of the World' by Robert Jordan,
"For all that spring should have come a good month since, the wind carried an icy chill as if it would rather bear snow."
The second part of this compound sentence is clear to me. However, I am unable to understand the meaning of the subordinate clause with which the sentence starts "For all that ... since,". Please clarify the meaning of this part and as it occurs to me that the word 'since' has been used in a way I have not seen before, so if there are similar examples of usage of 'since', please mention them as well. And also exemplify this kind of sentence structure, "For all that ... since, the main clause."