Over 40, 000 lead seals from the early Byzantine Empire remain today  Apart from the rare cases where the seal authenticated a document of special importance, most seals had served their purpose when the document was opened  Lead was not expensive, but it was not free: most lead seals would have been recast once they had served their purpose
Thus the number of early Byzantine documents sealed in such a fashion must have been many times the number of remaining lead seals
Most of the lead seals produced during the early Byzantine Empire were affixed to documents that were then opened during that period.