Hi,
I currently can't remember a specific regulation requiring the label to show the revision level (when it can't be considered IFU). However, labels are (or at least ought to be) controlled documents, and as such I would expect them to show the revision level. Perhaps your answer hides in the Document Control regulations and/ot guidance.
I don't particularly agree that a label should bear the revision level (or even any identification marks), just because it's a medical device component, or even a very important one. Of course this could make a lot of sense, but I'm not currently aware of a related regulatory requirement across the board. For instance, many plastic parts of many devices bear no identification marks, even though their design is controlled and they go through numerous and/or frequent design revisions. Such parts are controlled and implementation of the current revision is ensured via a host of means, according to the criticality / possibility of getting it wrong. So in theory the same could be done with labels.
In fact, in the pharma industry it's a common requirement that the labels issued for each and every batch are visually proofed by more than one competent person against the current master, to make sure that no discrepancies are present, for whatever reason (including using an outdated revision). The typical instructions require visual inspection of all details to ensure that they are identical; this goes well beyond just verifying the revision level.
Cheers,
Ronen.