Following this link here: https://shkspr.mobi/blog/2021/06/where-is-the-original-overv...
In a comment at the bottom it references a paper published by a few people working jointly with Computer Corporation of America, MIT & Boston University.
If you view that referenced paper "Correctness Conditions for Highly Available Databases" by N. Lynch, B. Blaustein & M. Siegel (https://apps.dtic.mil/sti/pdfs/ADA171427.pdf), and look at section 1.2 it clearly describes "SHARD: (System for Highly Available Replicated Data)" as being underdevelopment at CCA. It also says if you want to learn more about Shard, see the paper's reference [SBK]. Checking out the references section of that paper it lists the following for [SBK]:
Sarin, S. K., Blaustein, B. T., and Kaufman, C. W., "System Architecture for Partition Tolerant Distributed Databases," IEEE Transactions on Computers C-34, 12 (December 1985). pp. 1158-1163.
Which means there was a paper published in 1985, describing the in development Shard system.
It is possible that in 1985 they hadn't yet named the system "Shard", and it only got that name by 1988 - but it'd be interesting to check out that 1985 paper and see if they used the term Shard at all.