You can find reports from before 1988 mentioning SHARD being in development, like the one from June 1986 linked in this sister comment: https://news.ycombinator.com/item?id=36849634
Some more, from 1989[1][2][3]. Which again, reference the missing "SHARD" paper, but contain enough detail to make it clear that the idea of SHARD existed, regardless of the status of that particular document.
[1]: https://apps.dtic.mil/sti/tr/pdf/ADA214478.pdf
[2]: https://apps.dtic.mil/sti/tr/pdf/ADA216523.pdf
[3]: https://apps.dtic.mil/sti/tr/pdf/ADA209437.pdf