«أَلْفٌ مِنْ نَقْدِ الْبَلَدِ»
“One thousand in the currency of the locality.”
If a person acknowledges owing “one thousand,” the locally circulating currency may already be the apparent meaning, though another currency might conceivably be intended. Confirming that the sum refers to the local currency strengthens the interpretation favored by custom.
Here customary usage supplies the original apparent sense, and the subsequent words confirm it. If, by contrast, the first wording does not disclose the kind of object at all, a later identification of the object is explanatory tafsir. What matters is how much the first statement disclosed.