Wrong ItemID in GetItemID |Classic OPC: DA, A&E, HDA, XML-DA, etc.|Forum|OPC Foundation

While browsing OPC DA tree, my .NET app gets the OPC_E_UNKNOWNITEMID error on several sub branches during calling AddItems API. I added more logs and saw that the result of GetItemID API call differs from one that I could get if I would concatenate all parent names of a tag. For example,

GetItemID result: FPA.Fire Panel -.Detector.54.MyTagName

Concatenated parent names: FPA.Fire Panel 1-1.Detector.MyTagName

Using the latter form, I successfully subscribe to tag updates via AddItems call. The former form raises the OPC_E_UNKNOWNITEMID error.