Signal words for the Past Perfect Continuous

What are signal words for the Past Perfect Continuous?

There are no signal words solely for the Past Perfect Continuous, but we often use the Past Perfect Continuous together with Past Simple. Watch out when two actions in the past are combined.

The following words/phrases can indicate that Past Perfect Continuous could be used:

• already
• before
• for
• just
• never
• not yet
• once
• until that day
• when