Do bailiffs knock and then leave without leaving a document during the enforcement stage?

Yes

Unless the bailiff takes control of goods, there is no need for them to leave a document telling you they have attended.^[1]

Bailiffs often leave a document hanging out of the letterbox. This enables them to return at a later date to see if anyone has returned and taken in the document. A tactic often used by burglars when looking for a target property.^[2]

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^{[1] Regulation 30 of the Taking Control of Goods Regulations 2013
[2] Why bailiffs leave documents hanging from letterboxes or in a communal entrance}