I have a google sheet where

• col A is an imported list of TRUE/FALSE values
• col B is a series of incrementing integers which resets as T->F or F->T
• Col C is either an integer that is unrelated to col B OR it is blank OR it is one of a few string values.
• col D is equal to colB when col C is blank or an integer OR static at the most recent integer value of col B when col C is a string OR continues counting up from the static value until col B resets again
• When col A is FALSE, col C will be null and cols B and D will match