Except they did say the drop rate for the chases.
Emperor's Shuttle thread:
"This new ship's blueprints have a drop rate of 4% per point of Ship Energy per attempt (8 = 32%, 10 = 40%, 16 = 64%, 20 = 80%). Please note that each attempt is an independent event."
Adjusted GC Shard Drop Rate:
"Back in July of last year, we changed the refresh rate and cost of Ship Energy to match regular Energy. This cut the refresh rate and cost of refreshes for Ship energy in half and Galactic Chase drop rates on Fleet nodes were adjusted from 4% to 2% to account for these changes. This does not change the drop rate for any other types of nodes that Galactic Chases can appear on."