Thanks Rafal!

Must have been an interesting time. Wet Collodion was better than any dry plates, but inconvenient. Amateurs demanded the more convenient dry plates even if it meant they were slower than what the pros used. And there were general quality and consistency issues that had to be resolved too...

(Your post led me to a preview online of .. Encyclopedia of 19th Century Photography By John Hannavy pg. 438 which briefly mentions H&D emulsion speed in a chapter on dry plate gelatin negatives)