Function with_suffix 

fn with_suffix(desc: &str, suffix: &str) -> String

describe with the derived-series suffix folded into the name, so a .count series reports the name a caller can query it back by.

That is only true because collect_block strips a DERIVED suffix when the descriptor dictionary does not hold the requested name. Emitting a name here that the filter there does not accept is the same bug as returning a cursor nobody can page with.