What Rix says is correct as I remember reading how GM had what they called their 'engine deproliferation program' before 1970 production, deleting as many similar suffixes as possible. . Inventory of so many different suffixes was a problem also keeping them all in the pipeline so if an engine was close to what they wanted, it was slated for production and the 'excess' suffix motors dropped. . Comparing how many total suffixes were offered between '69 & '70 should show a big difference. .
~ Pete